io_uring: better ref handling in poll_remove_one

Instead of io_put_req() to drop not a final ref, use req_ref_put(),
which is slimmer and will also check the invariant.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/85b5774ce13ae55cc2e705abdc8cbafe1212f1bd.1617287883.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -5244,7 +5244,7 @@ static bool io_poll_remove_waitqs(struct io_kiocb *req)
 		/* non-poll requests have submit ref still */
 		do_complete = __io_poll_remove_one(req, &apoll->poll, true);
 		if (do_complete) {
-			io_put_req(req);
+			req_ref_put(req);
 			kfree(apoll->double_poll);
 			kfree(apoll);
 		}