io_uring: add IOPOLL and reserved field checks to IORING_OP_RENAMEAT

We can't support IOPOLL with non-pollable request types, and we should
check for unused/reserved fields like we do for other request types.

Fixes: 80a261fd

 ("io_uring: add support for IORING_OP_RENAMEAT")
Cc: stable@vger.kernel.org
Reported-by: Dmitry Kadashev <dkadashev@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>