tests/nouveau/threaded: adapt ioctl signature for FreeBSD

FreeBSD also use (int, unsigned long int, ...) like GLIBC.

Signed-off-by: Emmanuel Vadot <manu@FreeBSD.org>
Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>