io_uring: check that data field is 0 in ringfd unregister

Only allow data field to be 0 in struct io_uring_rsrc_update user
arguments to allow for future possible usage.

Fixes: e7a6c00d ("io_uring: add support for registering ring file descriptors")
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
Link: https://lore.kernel.org/r/20220429142218.GA28696@asgard.redhat.com


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