The hostel with the shortest distance to HKG appears to be the YHA Ngong Ping SG Davis Hostel, but not very practical to get there late at night (or even during the day).
If not sleeping at the airport you'll have to go to Mong Kok or TST. If arriving after midnight you can take the N21 bus which runs every 20 minutes, though don't know if hostels typically have 24-hour front desk....