[S390] cio: introduce cio_update_schib

There is the chance that we get condition code 0 for a stsch but
the resulting schib is not vaild. In the current code there are
2 cases:
* we do a check for validity of the schib after stsch, but at this
  time we have already stored the invaild schib in the subchannel
  structure. This may lead to problems.
* we don't do a check for validity, which is not that good either.

The patch addresses both issues by introducing the stsch wrapper
cio_update_schib which performs stsch on a local schib. This schib
is only written back to the subchannel if it's valid.

side note: For some functions (chp_events) the return codes are
different now (-ENXIO vs -ENODEV) but this shouldn't do harm
since the caller doesn't check for _specific_ errors.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/cio/device_pgid.c

@@ -504,7 +504,7 @@ ccw_device_verify_start(struct ccw_device *cdev)
 	sch->vpm = 0;
 
 	/* Get current pam. */
-	if (stsch(sch->schid, &sch->schib)) {
+	if (cio_update_schib(sch)) {
 		ccw_device_verify_done(cdev, -ENODEV);
 		return;
 	}