scsi: libsas: always unregister the old device if going to discover new

If we went into sas_rediscover_dev() the attached_sas_addr was already insured
not to be zero. So it's unnecessary to check if the attached_sas_addr is zero.

And although if the sas address is not changed, we always have to unregister
the old device when we are going to register a new one. We cannot just leave
the device there and bring up the new.

Signed-off-by: Jason Yan <yanaijie@huawei.com>
CC: chenxiang <chenxiang66@hisilicon.com>
CC: John Garry <john.garry@huawei.com>
CC: Johannes Thumshirn <jthumshirn@suse.de>
CC: Ewan Milne <emilne@redhat.com>
CC: Christoph Hellwig <hch@lst.de>
CC: Tomas Henzl <thenzl@redhat.com>
CC: Dan Williams <dan.j.williams@intel.com>
CC: Hannes Reinecke <hare@suse.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>