Fix compile error with ref_mv disabled

Change-Id: I6c5a843df7de0e711db27ccc5cfbe9fde8d6bae4

av1/common/entropymv.c

diff --git a/av1/common/entropymv.c b/av1/common/entropymv.c
index f01a3f7..8d011ea 100644
--- a/av1/common/entropymv.c
+++ b/av1/common/entropymv.c
@@ -222,10 +222,9 @@
 }
 
 void av1_adapt_mv_probs(AV1_COMMON *cm, int allow_hp) {
-  int i;
+  int i, j;
 #if CONFIG_REF_MV
   int idx;
-  int j;
   for (idx = 0; idx < NMV_CONTEXTS; ++idx) {
     nmv_context *fc = &cm->fc->nmvc[idx];
     const nmv_context *pre_fc =