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>
diff --git a/drivers/nvdimm/blk.c b/drivers/nvdimm/blk.c
index 0df77cb..91a336e 100644
--- a/drivers/nvdimm/blk.c
+++ b/drivers/nvdimm/blk.c
@@ -161,7 +161,7 @@
 	return err;
 }
 
-static void nd_blk_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t nd_blk_make_request(struct request_queue *q, struct bio *bio)
 {
 	struct block_device *bdev = bio->bi_bdev;
 	struct gendisk *disk = bdev->bd_disk;
@@ -208,6 +208,7 @@
 
  out:
 	bio_endio(bio);
+	return BLK_QC_T_NONE;
 }
 
 static int nd_blk_rw_bytes(struct nd_namespace_common *ndns,