bcm2835_clock_rate_from_divisor
rate = bcm2835_clock_rate_from_divisor(clock, parent_rate, div);
*avgrate = bcm2835_clock_rate_from_divisor(clock, *prate, *div);
high = bcm2835_clock_rate_from_divisor(clock, *prate,
low = bcm2835_clock_rate_from_divisor(clock, *prate,