io_uring: update outdated comment of callbacks

Previous commit ebc11b6c ("io_uring: clean io-wq callbacks") rename
io_free_work() into io_wq_free_work() for consistency. This patch also
updates relevant comment to avoid misunderstanding.

Fixes: ebc11b6c ("io_uring: clean io-wq callbacks")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
Link: https://lore.kernel.org/r/20221110122103.20120-1-linma@zju.edu.cnSigned-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.c

@@ -1781,7 +1781,7 @@ void io_wq_submit_work(struct io_wq_work *work)
 	bool needs_poll = false;
 	int ret = 0, err = -ECANCELED;
 
-	/* one will be dropped by ->io_free_work() after returning to io-wq */
+	/* one will be dropped by ->io_wq_free_work() after returning to io-wq */
 	if (!(req->flags & REQ_F_REFCOUNT))
 		__io_req_set_refcount(req, 2);
 	else