Add a forward declaration of mpeg1_decode_block_intra to fix compilation

broken by r18859 for e.g. all gcc 4 compilers.

Originally committed as revision 18861 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpeg12.c

@@ -49,6 +49,9 @@
 #define MB_PTYPE_VLC_BITS 6
 #define MB_BTYPE_VLC_BITS 6
 
+static inline int mpeg1_decode_block_intra(MpegEncContext *s,
+                              DCTELEM *block,
+                              int n);
 static inline int mpeg1_decode_block_inter(MpegEncContext *s,
                               DCTELEM *block,
                               int n);