Move IORING_SETUP_IOPOLL check into __io_openat_prep(), so both openat
and openat2 reuse it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/9a73ce83e4ee60d011180ef177eecef8e87ff2a2.1628471125.git.asml.silence@gmail.com


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