mpegaudiodec/mp3on4: fix buffer size.

The larger (and really ugly) size is not needed anymore.

Found-by: Justin Ruggles
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mpegaudiodec.c

@@ -1934,7 +1934,7 @@ static int decode_frame_mp3on4(AVCodecContext *avctx, void *data,
     int fr, ch, ret;
 
     /* get output buffer */
-    s->frame->nb_samples = s->frames * MPA_FRAME_SIZE;
+    s->frame->nb_samples = MPA_FRAME_SIZE;
     if ((ret = ff_get_buffer(avctx, s->frame)) < 0) {
         av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
         return ret;