block: add end_queued_request() and end_dequeued_request() helpers

We can use this helper in the elevator core for BLKPREP_KILL, and it'll
also be useful for the empty barrier patch.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/elevator.c b/block/elevator.c
index b9c518a..ec23ca0 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -751,15 +751,8 @@
 			rq = NULL;
 			break;
 		} else if (ret == BLKPREP_KILL) {
-			int nr_bytes = rq->hard_nr_sectors << 9;
-
-			if (!nr_bytes)
-				nr_bytes = rq->data_len;
-
-			blkdev_dequeue_request(rq);
 			rq->cmd_flags |= REQ_QUIET;
-			end_that_request_chunk(rq, 0, nr_bytes);
-			end_that_request_last(rq, 0);
+			end_queued_request(rq, 0);
 		} else {
 			printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
 								ret);