io_uring: remove superfluous check for sqe->off in io_accept()

This field contains a pointer to addrlen and checking to see if it's set
returns -EINVAL if the caller sets addr & addrlen pointers.

Fixes: 17f2fe35 ("io_uring: add support for IORING_OP_ACCEPT")
Signed-off-by: Hrvoje Zeba <zeba.hrvoje@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>