Refine mv equal check by using int_mv

Use union can check two MVs' equality by one
statement, no need to check col and row separately.

Change-Id: I94120435bc3f7bb3d3aa595f2c7c75a8c7579d87
diff --git a/av1/encoder/block.h b/av1/encoder/block.h
index bbd5734..28cc1b4 100644
--- a/av1/encoder/block.h
+++ b/av1/encoder/block.h
@@ -169,7 +169,7 @@
 #define MAX_INTERP_FILTER_STATS 64
 typedef struct {
   InterpFilters filters;
-  MV mv[2];
+  int_mv mv[2];
   int8_t ref_frames[2];
 } INTERPOLATION_FILTER_STATS;