block: remove __blk_put_request()

Now there's no difference between blk_put_request() and
__blk_put_request() anymore, get rid of the underscore version and
convert the few callers.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Tested-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-merge.c b/block/blk-merge.c
index c068c30..3d07330 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -866,7 +866,7 @@ int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 
 	free = attempt_merge(q, rq, next);
 	if (free) {
-		__blk_put_request(q, free);
+		blk_put_request(free);
 		return 1;
 	}