Bugfix: reduce MAX_MAX_DRL_BITS

this fix issue #798, the MAX_MAX_DRL_BITS should be reduced to 5, becuase now the DRL size is up to 6

STATS_CHANGED
diff --git a/av1/common/enums.h b/av1/common/enums.h
index 6aa12f5..1c81098 100644
--- a/av1/common/enums.h
+++ b/av1/common/enums.h
@@ -987,7 +987,11 @@
 #define COMP_GROUP_IDX_CONTEXTS 12
 
 #define MIN_MAX_DRL_BITS 1
+#if CONFIG_DRL_SIZE_LIMIT
+#define MAX_MAX_DRL_BITS 5
+#else
 #define MAX_MAX_DRL_BITS 7
+#endif
 
 #if !CONFIG_OPT_INTER_MODE_CTX
 #define NMV_CONTEXTS 3