blk-iocost: simplify ioc_name

Just directly dereference the disk name instead of going through multiple
hoops to find the same value.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Andreas Herrmann <aherrmann@suse.de>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20220921180501.1539876-10-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-iocost.c

@@ -664,17 +664,13 @@ static struct ioc *q_to_ioc(struct request_queue *q)
 	return rqos_to_ioc(rq_qos_id(q, RQ_QOS_COST));
 }
 
-static const char *q_name(struct request_queue *q)
-{
-	if (blk_queue_registered(q))
-		return kobject_name(q->kobj.parent);
-	else
-		return "<unknown>";
-}
-
 static const char __maybe_unused *ioc_name(struct ioc *ioc)
 {
-	return q_name(ioc->rqos.q);
+	struct gendisk *disk = ioc->rqos.q->disk;
+
+	if (!disk)
+		return "<unknown>";
+	return disk->disk_name;
 }
 
 static struct ioc_gq *pd_to_iocg(struct blkg_policy_data *pd)