If no driver is attached to a device or the driver provides no
set_online/set_offline function, setting this device online/offline
via its sysfs online attribute will silently fail but return success.

This patch changes the behavior to return -EINVAL in those cases.
Signed-off-by: NSebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>