Revert "tools/uncoded_frame: remove usage of avfilter_link_get_channels()"

This reverts commit 01c21653.

It was applied by accident before it could be reviewed.

tools/uncoded_frame.c

@@ -178,7 +178,7 @@ int main(int argc, char **argv)
             break;
         case AVMEDIA_TYPE_AUDIO:
             st->stream->codec->channel_layout = st->link->channel_layout;
-            st->stream->codec->channels = st->link->channels;
+            st->stream->codec->channels = avfilter_link_get_channels(st->link);
             st->stream->codec->sample_rate = st->link->sample_rate;
             st->stream->codec->sample_fmt = st->link->format;
             st->stream->codec->codec_id =