scsi: check request was requeued before scheduling requeue work

blk_requeue_request() may not always actually requeue the request.
Verify request was requeued before scheduling the requeue work.

Change-Id: I5de4cb0df00aa0c5dc66a4faad71fa04446f6545
Signed-off-by: Gilad Broner <gbroner@codeaurora.org>