sbp2: fix deregistration of status fifo address space

The proper designator of an invalid CSR address is ~(u64)0, not (u64)0.
Use the correct value in initialization and deregistration.
Also, scsi_id->sbp2_lun does not need to be initialized twice.
(scsi_id was kzalloc'd.)

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Ben Collins <bcollins@ubuntu.com>