Servo library should use peripheral clock frequency (80MHz) instead of F_CPU

[mytrain]

When running the following timer1 configuration, 'timerTick' is still invoked with a period of 50 us whatever the CPU frequency 160Mz or 80Mhz
timer1_isr_init();
timer1_attachInterrupt(timerTick);
timer1_enable(TIM_DIV16, TIM_EDGE, TIM_LOOP);
timer1_write(250);

I assumed that CPU frequency is changed correctly in the IDE as clockCyclesPerMicrosecond() returns 80 (for 80Mhz) or 160 (for 160Mhz).

As consequence (not tested by myself) ServoTimer.h code should not work properly in case of 160Mhz setup.