Now we are processing sas event and discover event in different
workqueues.  It's safe to wait the discover event done in the sas event
work. Use flush_workqueue() to insure the disco and revalidate events
processed synchronously so that the whole discover and revalidate
process will not be interrupted by other events.
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: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>