io_uring: fix incorrect unlikely() usage in io_waitid_prep()

The negation operator is incorrectly placed outside the unlikely()
macro:

    if (!unlikely(iwa))

This inverts the compiler branch prediction hint, marking the NULL case
as likely instead of unlikely. The intent is to indicate that allocation
failures are rare, consistent with common kernel patterns.

 Moving the negation inside unlikely():

    if (unlikely(!iwa))

Fixes: 2b4fc4c ("io_uring/waitid: setup async data in the prep handler")
Signed-off-by: Alok Tiwari <[email protected]>
Reviewed-by: Gabriel Krisman Bertazi <[email protected]>
Reviewed-by: Caleb Sander Mateos <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

Author: aloktiwa

io_uring/waitid.c

@@ -250,7 +250,7 @@ int io_waitid_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 		return -EINVAL;
 
 	iwa = io_uring_alloc_async_data(NULL, req);
-	if (!unlikely(iwa))
+	if (unlikely(!iwa))
 		return -ENOMEM;
 	iwa->req = req;