Use #define statement for MAX_MB_PLANE

Change-Id: I3a7f83ab1dbfcedc8a82fe798c2fa30dd9c7d696
diff --git a/vp9/common/vp9_blockd.h b/vp9/common/vp9_blockd.h
index 9e79ba0..4eb8b1a 100644
--- a/vp9/common/vp9_blockd.h
+++ b/vp9/common/vp9_blockd.h
@@ -47,6 +47,8 @@
   PLANE_TYPES
 } PLANE_TYPE;
 
+#define MAX_MB_PLANE 3
+
 typedef char ENTROPY_CONTEXT;
 
 static INLINE int combine_entropy_contexts(ENTROPY_CONTEXT a,
@@ -160,8 +162,6 @@
   MV_PRECISION_Q4
 };
 
-enum { MAX_MB_PLANE = 3 };
-
 struct buf_2d {
   uint8_t *buf;
   int stride;