By Starting the timer when period was set to 0, the SCTimer was giving
control of the pin back to the timer and over-riding the value written
to base->OUTPUT register. Consequently, the PWM timer was never
stopped and still using the previously configured period.
The PWM now correctly stops when setting the period to 0.
Signed-off-by: Guy Morand <guy.morand@bytesatwork.ch>