Return 0 on read from PIT control port. Intel explicitly says this is not

Return 0 on read from PIT control port. Intel explicitly says this is not
supported, and it looks like other emulators/hypervisors do a variety of
different things here. Most return 0, but at least one might return random
garbage. Returning 0 seems safest here, but leave a warning in place for
the logs in case a guest VM does this.