Verify that the user does not pass in anything but 0 for this field.

Fixes: 992da01a ("io_uring: change registration/upd/rsrc tagging ABI")
Signed-off-by: NDylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220412163042.2788062-3-dylany@fb.comSigned-off-by: NJens Axboe <axboe@kernel.dk>