cciss: Fix problem with remove_from_scan_list on driver unload

cciss: Fix problem with remove_from_scan_list that on driver unload
it doesn't remove the controller from the scan list correctly if
the controller is currently being scanned for new devices.

Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>