fftools/ffplay: use correct buffersink channel layout parameters

Regression since 0995e1f1b3.

Signed-off-by: Marton Balint <cus@passwd.hu>
(cherry picked from commit 7251f90972)

fftools/ffplay.c

@@ -1998,6 +1998,8 @@ static int configure_audio_filters(VideoState *is, const char *afilters, int for
         goto end;
 
     if (force_output_format) {
+        av_bprint_clear(&bp);
+        av_channel_layout_describe_bprint(&is->audio_tgt.ch_layout, &bp);
         sample_rates   [0] = is->audio_tgt.freq;
         if ((ret = av_opt_set_int(filt_asink, "all_channel_counts", 0, AV_OPT_SEARCH_CHILDREN)) < 0)
             goto end;