Release old elevator on change elevator

static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size)

{

	struct request_queue *rq;

	elevator_t *old_e;

	rq = blk_init_queue(do_blkif_request, &blkif_io_lock);

	if (rq == NULL)

		return -1;

	elevator_init(rq, "noop");

	old_e = rq->elevator;

	if (IS_ERR_VALUE(elevator_init(rq, "noop")))

		printk(KERN_WARNING

			"blkfront: Switch elevator failed, use default\n");

	else

		elevator_exit(old_e);

	/* Hard sector size and max sectors impersonate the equiv. hardware. */

	blk_queue_hardsect_size(rq, sector_size);