the example decode_audio.c does not compile

[rabijl]

Summary of the bug:

I tried to compile the examples in doc/examples, however the decode_audio.c errors when compiling. This is the error generated:

```
cc  -Wall -g   -c -o decode_audio.o decode_audio.c
decode_audio.c: In function ‘decode’:
decode_audio.c:101:54: error: request for member ‘nb_channels’ in something not a structure or union
  101 |             for (ch = 0; ch < dec_ctx->channel_layout.nb_channels; ch++)
      |                                                      ^
decode_audio.c: In function ‘main’:
decode_audio.c:219:35: error: request for member ‘nb_channels’ in something not a structure or union
  219 |     n_channels = c->channel_layout.nb_channels;
      |                                   ^
make: *** [<builtin>: decode_audio.o] Error 1

``` 
I tried this on both ubuntu and arch and got the same result

How to reproduce:

% run `make -f Makefile.example` in the master branch of ffmpeg 
ffmpeg version: 4.4.2-0ubuntu0.22.04.1
built on: ubuntu 22.04 lts
cc version:(Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0

Patches should be submitted to the ffmpeg-devel mailing list and not this bug tracker.

[rabijl]

I Figured out that I forgot to checkout the correct tag. feel free to delete this ticket