merge/simplify 2 if()

~4 cpu cylces faster for the matrixbench video

Originally committed as revision 9856 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpeg12.c

@@ -366,11 +366,7 @@ static int mpeg_decode_mb(MpegEncContext *s,
                 motion_type = MT_FRAME;
             else{
                 motion_type = get_bits(&s->gb, 2);
-            }
-
-            /* compute dct type */
-            if (s->picture_structure == PICT_FRAME && //FIXME add a interlaced_dct coded var?
-                !s->frame_pred_frame_dct && HAS_CBP(mb_type)) {
+                if (s->picture_structure == PICT_FRAME && HAS_CBP(mb_type))
                     s->interlaced_dct = get_bits1(&s->gb);
             }