test/register-restrictions: don't fail if restrictions aren't supported
test/register-restrictions: don't fail if restrictions aren't supported

Also cleanup the tests a bit (static, void).

Signed-off-by: Jens Axboe <cd8c6775e60d6f67a6984377324e5290df3d5358@kernel.dk>

axboe/liburing,axboe/liburing,axboe/liburing