Change the type of pblocks from pointers to short array into

pointers to array of 64 DCTELEM, similarly to other block fields.
This also get rid of some casts and fixes a warning.

Originally committed as revision 17517 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegvideo.h

@@ -635,7 +635,7 @@ typedef struct MpegEncContext {
 
     uint8_t *ptr_lastgob;
     int swap_uv;//vcr2 codec is mpeg2 varint with UV swaped
-    short * pblocks[12];
+    DCTELEM (*pblocks[12])[64];
 
     DCTELEM (*block)[64]; ///< points to one of the following blocks
     DCTELEM (*blocks)[8][64]; // for HQ mode we need to keep the best block