some const

Originally committed as revision 11774 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/svq1dec.c

@@ -641,7 +641,7 @@ static int svq1_decode_frame_header (GetBitContext *bitbuf,MpegEncContext *s) {
 
 static int svq1_decode_frame(AVCodecContext *avctx,
                              void *data, int *data_size,
-                             uint8_t *buf, int buf_size)
+                             const uint8_t *buf, int buf_size)
 {
   MpegEncContext *s=avctx->priv_data;
   uint8_t        *current, *previous;