Fix conflict between lv_map and cb4x4

Change-Id: I0512000554ef74d397332e5ed135fe20e2c4a37e

av1/encoder/encodetxb.c

diff --git a/av1/encoder/encodetxb.c b/av1/encoder/encodetxb.c
index 7316420..9f1e729 100644
--- a/av1/encoder/encodetxb.c
+++ b/av1/encoder/encodetxb.c
@@ -184,9 +184,14 @@
   struct macroblockd_plane *pd = &xd->plane[plane];
 
 #if CONFIG_CB4X4
+#if CONFIG_CHROMA_2X2
   const BLOCK_SIZE plane_bsize = get_plane_block_size(bsize, pd);
 #else
   const BLOCK_SIZE plane_bsize =
+      AOMMAX(BLOCK_4X4, get_plane_block_size(bsize, pd));
+#endif  // CONFIG_CHROMA_2X2
+#else
+  const BLOCK_SIZE plane_bsize =
       get_plane_block_size(AOMMAX(bsize, BLOCK_8X8), pd);
 #endif
   const int max_blocks_wide = max_block_wide(xd, plane_bsize, plane);