Make get_tx_type() to support cb4x4 mode

The bmi structure for sub8x8 block is deprecated in the cb4x4 mode.
Always fetch the transform type from coding block's mode_info
structure directly.

Change-Id: I8df8536e1a1723b292600018c4843e5fcc025284

av1/common/blockd.h

diff --git a/av1/common/blockd.h b/av1/common/blockd.h
index b71c997..9fd5510 100644
--- a/av1/common/blockd.h
+++ b/av1/common/blockd.h
@@ -826,7 +826,7 @@
   if (xd->lossless[mbmi->segment_id] || txsize_sqr_map[tx_size] >= TX_32X32)
 #endif
     return DCT_DCT;
-  if (mbmi->sb_type >= BLOCK_8X8) {
+  if (mbmi->sb_type >= BLOCK_8X8 || CONFIG_CB4X4) {
     if (plane_type == PLANE_TYPE_Y) {
 #if !ALLOW_INTRA_EXT_TX
       if (is_inter_block(mbmi))
@@ -840,6 +840,10 @@
                  : mbmi->tx_type;
   }
 
+#if CONFIG_CB4X4
+  return DCT_DCT;
+#endif
+
   // Sub8x8-Inter/Intra OR UV-Intra
   if (is_inter_block(mbmi))  // Sub8x8-Inter
     return DCT_DCT;