[S390] cio: Fix race for "fast" path gone/path back situations.

Make sure we wait for previous evaluations triggered by path state
changes to have settled before we manipulate path states again.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
diff --git a/drivers/s390/cio/css.h b/drivers/s390/cio/css.h
index b705545..e191351 100644
--- a/drivers/s390/cio/css.h
+++ b/drivers/s390/cio/css.h
@@ -144,6 +144,7 @@
 int css_sch_is_valid(struct schib *);
 
 extern struct workqueue_struct *slow_path_wq;
+void css_wait_for_slow_path(void);
 
 extern struct attribute_group *subch_attr_groups[];
 #endif