blk: move blk_delete_timer call in end_that_request_last

Move the calling  blk_delete_timer to later in end_that_request_last to
address an issue where blkdev_dequeue_request may have add a timer for the
request.

Signed-off-by: Mike Anderson <andmike@linux.vnet.ibm.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>