Make AMR-NB block size const and 8 bits.

Originally committed as revision 12278 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/libamr.c

@@ -444,7 +444,7 @@ static int amr_nb_decode_frame(AVCodecContext * avctx,
 {
     AMRContext *s = avctx->priv_data;
     uint8_t*amrData=buf;
-    static short block_size[16]={ 12, 13, 15, 17, 19, 20, 26, 31, 5, 0, 0, 0, 0, 0, 0, 0 };
+    static const uint8_t block_size[16]={ 12, 13, 15, 17, 19, 20, 26, 31, 5, 0, 0, 0, 0, 0, 0, 0 };
     enum Mode dec_mode;
     int packet_size;