cciss: Fix race between disk-adding code and interrupt handler

Fix race condition between cciss_init_one(), cciss_update_drive_info(),
and cciss_check_queues().

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