[S390] cio: Use device_schedule_callback() for removing disconnected devices.

We can't deregister disconnected and orphaned devices directly from
the online attribute's store method, but must take a detour.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>