ntb_hw_switchtec: make ntb_mw_set_trans() work when addr == 0

On switchtec_ntb_mw_set_trans() call, when (only) address == 0, it acts as
ntb_mw_clear_trans(). Fix this, since address == 0 and size != 0 is valid
combination for setting translation.
Signed-off-by: Alexander Fomichev <fomichev.ru@gmail.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

drivers/ntb/hw/mscc/ntb_hw_switchtec.c

@@ -306,7 +306,7 @@ static int switchtec_ntb_mw_set_trans(struct ntb_dev *ntb, int pidx, int widx,
 	if (rc)
 		return rc;
 
-	if (addr == 0 || size == 0) {
+	if (size == 0) {
 		if (widx < nr_direct_mw)
 			switchtec_ntb_mw_clr_direct(sndev, widx);
 		else