Check the 12v sensor value directly instead of waiting the state machine

If we only check the sensor state flag, when a abrupt shutdown occurs,
we'll have to run through the sensor event state machine at least 2
times before achieving a state that causes the P12vGOOD flag to be
cleared.
Since the payload task runs at a greater frequency than the sensors',
it'll try to power-up the payload again based on the erroneous sensor
state