blk-mq: constify struct blk_mq_ops

Constify all instances of blk_mq_ops, as they are never modified.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 517838b..f24ade33 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -4317,7 +4317,7 @@
 	return 0;
 }
 
-static struct blk_mq_ops rbd_mq_ops = {
+static const struct blk_mq_ops rbd_mq_ops = {
 	.queue_rq	= rbd_queue_rq,
 	.init_request	= rbd_init_request,
 };