avfilter_get_audio_buffer_ref_from_frame: fix handling of >8 channels

Found-by: inferno@chromium.org
Reported-by: Dale Curtis <dalecurtis@google.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/avcodec.c

@@ -102,7 +102,7 @@ AVFilterBufferRef *avfilter_get_audio_buffer_ref_from_frame(const AVFrame *frame
     }
 
     samplesref = avfilter_get_audio_buffer_ref_from_arrays_channels(
-        (uint8_t **)frame->data, frame->linesize[0], perms,
+        (uint8_t **)frame->extended_data, frame->linesize[0], perms,
         frame->nb_samples, frame->format, channels, layout);
     if (!samplesref)
         return NULL;