io_uring: store io_kiocb in wait->private

Store the io_kiocb in the private field instead of the poll entry, this
is in preparation for allowing multiple waitqueues.

No functional changes in this patch.
Signed-off-by: NJens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -3730,8 +3730,8 @@ static void io_poll_trigger_evfd(struct io_wq_work **workptr)
 static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
 			void *key)
 {
-	struct io_poll_iocb *poll = wait->private;
-	struct io_kiocb *req = container_of(poll, struct io_kiocb, poll);
+	struct io_kiocb *req = wait->private;
+	struct io_poll_iocb *poll = &req->poll;
 	struct io_ring_ctx *ctx = req->ctx;
 	__poll_t mask = key_to_poll(key);
 
@@ -3854,7 +3854,7 @@ static int io_poll_add(struct io_kiocb *req, struct io_kiocb **nxt)
 	/* initialized the list so that we can do list_empty checks */
 	INIT_LIST_HEAD(&poll->wait.entry);
 	init_waitqueue_func_entry(&poll->wait, io_poll_wake);
-	poll->wait.private = poll;
+	poll->wait.private = req;
 
 	INIT_LIST_HEAD(&req->list);