[NORMATIVE] Limit temporal MV storage to 13 bits

Modified REFMVS_LIMIT so that temporal MV storage uses 13 bits as suggested
in the issue.

BUG=aomedia:1532

Change-Id: Id7b81f899e5fb9afa62651bd700f544159659c36

av1/common/mvref_common.h

diff --git a/av1/common/mvref_common.h b/av1/common/mvref_common.h
index c94150c..b3affda 100644
--- a/av1/common/mvref_common.h
+++ b/av1/common/mvref_common.h
@@ -25,7 +25,7 @@
 // This would make a motion vector fit in 26 bits. Plus 3 bits for the
 // reference frame index. A tuple of motion vector can hence be stored within
 // 32 bit range for efficient load/store operations.
-#define REFMVS_LIMIT (1 << 12)
+#define REFMVS_LIMIT ((1 << 12) - 1)
 
 typedef struct position {
   int row;