io_uring/eventfd: check for the need to async notifier earlier

It's not necessary to do this post grabbing a reference. With that, we
can drop the out goto path as well.

Link: https://lore.kernel.org/r/20240921080307.185186-3-axboe@kernel.dk


Signed-off-by: Jens Axboe <axboe@kernel.dk>