block: change ->make_request_fn() and users to return a queue cookie

No functional changes in this patch, but it prepares us for returning
a more useful cookie related to the IO that was queued up.

Signed-off-by: Jens Axboe <axboe@fb.com>
Acked-by: Christoph Hellwig <hch@lst.de>
Acked-by: Keith Busch <keith.busch@intel.com>

arch/xtensa/platforms/iss/simdisk.c

@@ -101,7 +101,7 @@ static void simdisk_transfer(struct simdisk *dev, unsigned long sector,
 	spin_unlock(&dev->lock);
 }
 
-static void simdisk_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t simdisk_make_request(struct request_queue *q, struct bio *bio)
 {
 	struct simdisk *dev = q->queuedata;
 	struct bio_vec bvec;
@@ -119,6 +119,7 @@ static void simdisk_make_request(struct request_queue *q, struct bio *bio)
 	}
 
 	bio_endio(bio);
+	return BLK_QC_T_NONE;
 }
 
 static int simdisk_open(struct block_device *bdev, fmode_t mode)