Reduce txb_coeff_cost map size from 64 to 32

The maximum coding block size is 128 and the minimum tx size is
4. Using 32 per dimension to keep the txb coeff cost should be
safe.

Change-Id: Ie44fc581037f0d8270caec64543454701159eec5

av1/common/blockd.h

diff --git a/av1/common/blockd.h b/av1/common/blockd.h
index 06fed67..b10d7fd 100644
--- a/av1/common/blockd.h
+++ b/av1/common/blockd.h
@@ -197,7 +197,7 @@
 #endif  // CONFIG_FILTER_INTRA
 
 #if CONFIG_RD_DEBUG
-#define TXB_COEFF_COST_MAP_SIZE (2 * MAX_MIB_SIZE)
+#define TXB_COEFF_COST_MAP_SIZE (MAX_MIB_SIZE)
 #endif
 
 typedef struct RD_STATS {