small optimization

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@7327 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/vp6.c

@@ -343,7 +343,7 @@ static int vp6_block_variance(uint8_t *src, int stride)
         }
         src += 2*stride;
     }
-    return (16*square_sum - sum*sum) / (16*16);
+    return (16*square_sum - sum*sum) >> 8;
 }
 
 static void vp6_filter_hv2(vp56_context_t *s, uint8_t *dst, uint8_t *src,