Avoid using ADST for tx sizes > 16x16

When the reduced transform set is enabled in the frame level flag,
it is possible to select ADST for large tx sizes. This patch
corrects this issue.

BUG=aomedia:1280

Change-Id: I3c6166d0258cbf3179d74a911e420cea85e5299c

av1/common/blockd.h

@@ -763,10 +763,10 @@ static INLINE TxSetType get_ext_tx_set_type(TX_SIZE tx_size, BLOCK_SIZE bs,
 #else
   if (tx_size_sqr_up > TX_32X32 || bs < BLOCK_8X8) return EXT_TX_SET_DCTONLY;
 #endif  // USE_TXTYPE_SEARCH_FOR_SUB8X8_IN_CB4X4
-  if (use_reduced_set)
-    return is_inter ? EXT_TX_SET_DCT_IDTX : EXT_TX_SET_DTT4_IDTX;
   if (tx_size_sqr_up == TX_32X32)
     return is_inter ? EXT_TX_SET_DCT_IDTX : EXT_TX_SET_DCTONLY;
+  if (use_reduced_set)
+    return is_inter ? EXT_TX_SET_DCT_IDTX : EXT_TX_SET_DTT4_IDTX;
   if (is_inter) {
     return (tx_size_sqr == TX_16X16 ? EXT_TX_SET_DTT9_IDTX_1DDCT
                                     : EXT_TX_SET_ALL16);