[media-kit] media-plugins/alsa-plugins broken with ffmpeg upgrade

Nobody has claimed this yet.

```
/var/tmp/portage/media-plugins/alsa-plugins-1.2.7.1/work/alsa-plugins-1.2.7.1/a52/pcm_a52.c:1170:9: warning: ‘sample_fmts’ is deprecated [-Wdeprecated-declarations]
1170 | rec->av_format = rec->codec->sample_fmts[0];
| ^~~
In file included from /usr/include/libavcodec/avcodec.h:41,
from /var/tmp/portage/media-plugins/alsa-plugins-1.2.7.1/work/alsa-plugins-1.2.7.1/a52/pcm_a52.c:28:
/usr/include/libavcodec/codec.h:204:32: note: declared here
204 | const enum AVSampleFormat *sample_fmts; ///< @deprecated use avcodec_get_supported_config()
| ^~~~~~~~~~~
make[2]: *** [Makefile:468: pcm_a52.lo] Error 1
make[2]: Leaving directory '/var/tmp/portage/media-plugins/alsa-plugins-1.2.7.1/work/alsa-plugins-1.2.7.1-abi_x86_64.amd64/a52'
make[1]: *** [Makefile:444: all-recursive] Error 1
make[1]: Leaving directory '/var/tmp/portage/media-plugins/alsa-plugins-1.2.7.1/work/alsa-plugins-1.2.7.1-abi_x86_64.amd64'
make: *** [Makefile:376: all] Error 2
* ERROR: media-plugins/alsa-plugins-1.2.7.1::media-kit failed (compile phase):
* emake failed
*
```
The possible workaround is disable the `fffmpeg` USE for now.

It sounds good to autogen alsa packages because they are lovely old.

Start with media-plugins/alsa-plugins/a52/pcm_a52.c, especially the sample_fmts use shown in the build output, and reproduce the compile with the ffmpeg USE option enabled. Check the package build through the a52 directory and Makefile targets; done means alsa-plugins compiles successfully without requiring the reported workaround.

Written by the indexing model from the issue text.