package/mmc-utils: fix build failure due to a warning and -Werror enabled

Add patch to fix warning that is treated like error:
```
In function '__bswap_32',
    inlined from 'do_rpmb_write_block' at mmc_cmds.c:2293:27:
/home/autobuild/autobuild/instance-15/output-1/host/aarch64-buildroot-linux-gnu/sysroot/usr/include/bits/byteswap.h:52:10: error: 'cnt' may be used uninitialized [-Werror=maybe-uninitialized]
   52 |   return __builtin_bswap32 (__bsx);
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~
mmc_cmds.c: In function 'do_rpmb_write_block':
mmc_cmds.c:2270:22: note: 'cnt' was declared here
 2270 |         unsigned int cnt;
      |                      ^~~
cc1: all warnings being treated as errors
```
Patch is pending upstream:
https://patchwork.kernel.org/project/linux-mmc/patch/20220918124210.1127345-1-giulio.benetti@benettiengineering.com/

Fixes:
http://autobuild.buildroot.net/results/18c4fce5416e5d1ccd95900ccef87d4c045a361e/

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
---
 ...ds.c-fix-warning-on-uninitialized-cn.patch | 27 +++++++++++++++++++
 1 file changed, 27 insertions(+)
 create mode 100644 package/mmc-utils/0002-mmc-utils-mmc_cmds.c-fix-warning-on-uninitialized-cn.patch

Giulio, All,

On 2022-09-18 14:53 +0200, Giulio Benetti spake thusly:
> Add patch to fix warning that is treated like error:
> ```
> In function '__bswap_32',
>     inlined from 'do_rpmb_write_block' at mmc_cmds.c:2293:27:
> /home/autobuild/autobuild/instance-15/output-1/host/aarch64-buildroot-linux-gnu/sysroot/usr/include/bits/byteswap.h:52:10: error: 'cnt' may be used uninitialized [-Werror=maybe-uninitialized]
>    52 |   return __builtin_bswap32 (__bsx);
>       |          ^~~~~~~~~~~~~~~~~~~~~~~~~
> mmc_cmds.c: In function 'do_rpmb_write_block':
> mmc_cmds.c:2270:22: note: 'cnt' was declared here
>  2270 |         unsigned int cnt;
>       |                      ^~~
> cc1: all warnings being treated as errors
> ```
> Patch is pending upstream:
> https://patchwork.kernel.org/project/linux-mmc/patch/20220918124210.1127345-1-giulio.benetti@benettiengineering.com/

Arnd requested a different fix, arguing the one you proposed is hiding a
compiler warning without fixing the root cause.

Regards,
Yann E. MORIN.

> http://autobuild.buildroot.net/results/18c4fce5416e5d1ccd95900ccef87d4c045a361e/
> 
> Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
> ---
>  ...ds.c-fix-warning-on-uninitialized-cn.patch | 27 +++++++++++++++++++
>  1 file changed, 27 insertions(+)
>  create mode 100644 package/mmc-utils/0002-mmc-utils-mmc_cmds.c-fix-warning-on-uninitialized-cn.patch
> 
> diff --git a/package/mmc-utils/0002-mmc-utils-mmc_cmds.c-fix-warning-on-uninitialized-cn.patch b/package/mmc-utils/0002-mmc-utils-mmc_cmds.c-fix-warning-on-uninitialized-cn.patch
> new file mode 100644
> index 0000000000..e2f74879a6
> --- /dev/null
> +++ b/package/mmc-utils/0002-mmc-utils-mmc_cmds.c-fix-warning-on-uninitialized-cn.patch
> @@ -0,0 +1,27 @@
> +From bf783bbc2da0348591dd317ccd53bbfc5a57f2f8 Mon Sep 17 00:00:00 2001
> +From: Giulio Benetti <giulio.benetti@benettiengineering.com>
> +Date: Sun, 18 Sep 2022 14:10:29 +0200
> +Subject: [PATCH] mmc-utils: mmc_cmds.c: fix warning on uninitialized 'cnt'
> +
> +Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
> +[Upstream status: https://patchwork.kernel.org/project/linux-mmc/patch/20220918124210.1127345-1-giulio.benetti@benettiengineering.com/]
> +---
> + mmc_cmds.c | 2 +-
> + 1 file changed, 1 insertion(+), 1 deletion(-)
> +
> +diff --git a/mmc_cmds.c b/mmc_cmds.c
> +index 12b7802..777d649 100644
> +--- a/mmc_cmds.c
> ++++ b/mmc_cmds.c
> +@@ -2436,7 +2436,7 @@ int do_rpmb_write_block(int nargs, char **argv)
> + 	int ret, dev_fd, key_fd, data_fd;
> + 	unsigned char key[32];
> + 	uint16_t addr;
> +-	unsigned int cnt;
> ++	unsigned int cnt = 0;
> + 	struct rpmb_frame frame_in = {
> + 		.req_resp    = htobe16(MMC_RPMB_WRITE),
> + 		.block_count = htobe16(1)
> +-- 
> +2.34.1
> +
> -- 
> 2.34.1
> 
> _______________________________________________
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> buildroot@buildroot.org
> https://lists.buildroot.org/mailman/listinfo/buildroot

Hi Arnd,

On 18/09/22 17:37, Yann E. MORIN wrote:
> Giulio, All,
> 
> On 2022-09-18 14:53 +0200, Giulio Benetti spake thusly:
>> Add patch to fix warning that is treated like error:
>> ```
>> In function '__bswap_32',
>>      inlined from 'do_rpmb_write_block' at mmc_cmds.c:2293:27:
>> /home/autobuild/autobuild/instance-15/output-1/host/aarch64-buildroot-linux-gnu/sysroot/usr/include/bits/byteswap.h:52:10: error: 'cnt' may be used uninitialized [-Werror=maybe-uninitialized]
>>     52 |   return __builtin_bswap32 (__bsx);
>>        |          ^~~~~~~~~~~~~~~~~~~~~~~~~
>> mmc_cmds.c: In function 'do_rpmb_write_block':
>> mmc_cmds.c:2270:22: note: 'cnt' was declared here
>>   2270 |         unsigned int cnt;
>>        |                      ^~~
>> cc1: all warnings being treated as errors
>> ```
>> Patch is pending upstream:
>> https://patchwork.kernel.org/project/linux-mmc/patch/20220918124210.1127345-1-giulio.benetti@benettiengineering.com/
> 
> Arnd requested a different fix, arguing the one you proposed is hiding a
> compiler warning without fixing the root cause.

Yes, he's totally right and I've just re-spinned V3 patch:
https://lore.kernel.org/linux-mmc/20220918124210.1127345-1-giulio.benetti@benettiengineering.com/T/#mce3840c0bf84e1743552aa9428ef9097b613c610

Now I prepare send the V2 Buildroot patch.

Best regards

On 18/09/22 18:22, Giulio Benetti wrote:
> Hi Arnd,

s/Arnd/Yann sorry!