block: use req_op() to maintain consistency

This is a pure code cleanup patch and doesn't change any functionality.
In block layer to identify the request operation req_op() macro is
used, so change the open coding the req_op() in the blk-mq-debugfs.c.
Reviewed-by: NMartin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: NHannes Reinecke <hare@suse.com>
Signed-off-by: NChaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

block/blk-mq-debugfs.c

@@ -341,7 +341,7 @@ static const char *blk_mq_rq_state_name(enum mq_rq_state rq_state)
 int __blk_mq_debugfs_rq_show(struct seq_file *m, struct request *rq)
 {
 	const struct blk_mq_ops *const mq_ops = rq->q->mq_ops;
-	const unsigned int op = rq->cmd_flags & REQ_OP_MASK;
+	const unsigned int op = req_op(rq);
 
 	seq_printf(m, "%p {.op=", rq);
 	if (op < ARRAY_SIZE(op_name) && op_name[op])