scsi: libsas: add event to defer list tail instead of head when draining

Events will be added to defer_q list when setting ha->status to
SAS_HA_DRAINING. Events will be called after drain workqueue.

Those events are added to the head of list, but they are scanned one by
one from the head to the tail, which will cause those events be called
in the reverse order of being added. So change list_add to list_add_tail
in function sas_queue_work.

Signed-off-by: chenxiang <chenxiang66@hisilicon.com>
Signed-off-by: Jason Yan <yanaijie@huawei.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>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>