block/blk-rq-qos: Move a function from a header file into a C file

rq_qos_id_to_name() is only used in blk-mq-debugfs.c so move that function
into in blk-mq-debugfs.c.

Cc: Damien Le Moal <damien.lemoal@wdc.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Link: https://lore.kernel.org/r/20210618004456.7280-4-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq-debugfs.c

@@ -937,6 +937,19 @@ void blk_mq_debugfs_unregister_sched(struct request_queue *q)
 	q->sched_debugfs_dir = NULL;
 }
 
+static const char *rq_qos_id_to_name(enum rq_qos_id id)
+{
+	switch (id) {
+	case RQ_QOS_WBT:
+		return "wbt";
+	case RQ_QOS_LATENCY:
+		return "latency";
+	case RQ_QOS_COST:
+		return "cost";
+	}
+	return "unknown";
+}
+
 void blk_mq_debugfs_unregister_rqos(struct rq_qos *rqos)
 {
 	debugfs_remove_recursive(rqos->debugfs_dir);

block/blk-rq-qos.h

@@ -79,19 +79,6 @@ static inline struct rq_qos *blkcg_rq_qos(struct request_queue *q)
 	return rq_qos_id(q, RQ_QOS_LATENCY);
 }
 
-static inline const char *rq_qos_id_to_name(enum rq_qos_id id)
-{
-	switch (id) {
-	case RQ_QOS_WBT:
-		return "wbt";
-	case RQ_QOS_LATENCY:
-		return "latency";
-	case RQ_QOS_COST:
-		return "cost";
-	}
-	return "unknown";
-}
-
 static inline void rq_wait_init(struct rq_wait *rq_wait)
 {
 	atomic_set(&rq_wait->inflight, 0);