hwmon: (it87) Prevent power-off on Shuttle SN68PT

On the Shuttle SN68PT, FAN_CTL2 is apparently not connected to a fan,
but to something else. One user has reported instant system power-off
when changing the PWM2 duty cycle, so we disable it.

I use the board name string as the trigger in case the same board is
ever used in other systems.

This closes lm-sensors ticket #2349:
pwmconfig causes a hard poweroff
http://www.lm-sensors.org/ticket/2349

Signed-off-by: Jean Delvare <khali@linux-fr.org>