[S390] cio: Catch operand exceptions on stsch.

If we have a subchannel id which has been generated via
for_each_subchannel(), it might contain an invalid subchannel set id.
We need to catch the ensuing operand exception by using stsch_err()
instead of stsch() in all possible cases.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index 2da01b7..bdf1369 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -296,7 +296,7 @@
 		/* Will be done on the slow path. */
 		return -EAGAIN;
 	}
-	if (stsch(schid, &schib) || !schib.pmcw.dnv) {
+	if (stsch_err(schid, &schib) || !schib.pmcw.dnv) {
 		/* Unusable - ignore. */
 		return 0;
 	}