s390/ccwgroup: set_online return error when already online

Return -EINVAL if set_{on,off}line is called for already {on,off}line
devices. Also return -EINVAL for drivers which do not provide a callback
for set_{on,off}line. This behaviour is now consistent with the one for
ccw devices.

Reported-by: Stefan Raspl <[e-mail]>
Signed-off-by: Sebastian Ott <[e-mail]>
Acked-by: Peter Oberparleiter <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

drivers/s390/cio/ccwgroup.c

···
 static int ccwgroup_set_online(struct ccwgroup_device *gdev)
 {
 	struct ccwgroup_driver *gdrv = to_ccwgroupdrv(gdev->dev.driver);
-	int ret = 0;
+	int ret = -EINVAL;
 
 	if (atomic_cmpxchg(&gdev->onoff, 0, 1) != 0)
 		return -EAGAIN;
···
 static int ccwgroup_set_offline(struct ccwgroup_device *gdev)
 {
 	struct ccwgroup_driver *gdrv = to_ccwgroupdrv(gdev->dev.driver);
-	int ret = 0;
+	int ret = -EINVAL;
 
 	if (atomic_cmpxchg(&gdev->onoff, 0, 1) != 0)
 		return -EAGAIN;