[S390] cio: update descriptor in chsc_chp_vary

Update the channel path descriptor at the beginning of to the
vary_on operation.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/cio/chp.h b/drivers/s390/cio/chp.h
index 695ec20..12b4903 100644
--- a/drivers/s390/cio/chp.h
+++ b/drivers/s390/cio/chp.h
@@ -52,6 +52,12 @@
 	void *cmg_chars;
 };
 
+/* Return channel_path struct for given chpid. */
+static inline struct channel_path *chpid_to_chp(struct chp_id chpid)
+{
+	return channel_subsystems[chpid.cssid]->chps[chpid.id];
+}
+
 int chp_get_status(struct chp_id chpid);
 u8 chp_get_sch_opm(struct subchannel *sch);
 int chp_is_registered(struct chp_id chpid);