io_uring: refactor io_submit_sqe()

Remove one extra if for non-linked path of io_submit_sqe().

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/03183199d1bf494b4a72eca16d792c8a5945acb4.1650056133.git.asml.silence@gmail.com


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