sonicdec: fix frame size

Signed-off-by: NMichael Niedermayer <michaelni@gmx.at>

libavcodec/sonic.c

@@ -880,7 +880,7 @@ static int sonic_decode_frame(AVCodecContext *avctx,
 
     if (buf_size == 0) return 0;
 
-    s->frame.nb_samples = s->frame_size;
+    s->frame.nb_samples = s->frame_size / avctx->channels;
     if ((ret = ff_get_buffer(avctx, &s->frame, 0)) < 0)
         return ret;
     samples = (int16_t *)s->frame.data[0];