Put tx_type check into txk_sel config

Change-Id: I47a5eda017fe0d2592411eab621934eabeae7aa4

av1/encoder/encodetxb.c

diff --git a/av1/encoder/encodetxb.c b/av1/encoder/encodetxb.c
index f79981d..2576333 100644
--- a/av1/encoder/encodetxb.c
+++ b/av1/encoder/encodetxb.c
@@ -340,9 +340,11 @@
   (void)blk_col;
   aom_write_bin(w, eob == 0,
                 ec_ctx->txb_skip_cdf[txs_ctx][txb_ctx->txb_skip_ctx], 2);
+#if CONFIG_TXK_SEL
   if (plane == 0 && eob == 0) {
     assert(tx_type == DCT_DCT);
   }
+#endif
   if (eob == 0) return;
 
   av1_txb_init_levels(tcoeff, width, height, levels);