Fixed typo which caused incorrect motion prediction in B-frames. patch by (Loren Merritt <lorenm ta u tod washington tod edu>)

Originally committed as revision 3709 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h264.c

@@ -1017,7 +1017,7 @@ static inline void write_back_motion(H264Context *h, int mb_type){
                     }
                 }
                 for(y=0; y<2; y++){
-                    *(uint16_t*)s->current_picture.motion_val[list][b8_xy + y*h->b8_stride]= (LIST_NOT_USED&0xFF)*0x0101;
+                    *(uint16_t*)&s->current_picture.ref_index[list][b8_xy + y*h->b8_stride]= (LIST_NOT_USED&0xFF)*0x0101;
                 }
             }
             continue; //FIXME direct mode ...