Python example - Fixes emlid#28

After pwm-channel deinitialization some configurations seems to linger.
This causes pwm outputs to potentially get an unexpected behaviour.

By simply setting period to 1, the pwm output will behave as default
after deinitialization.

Python/navio/pwm.py

@@ -20,6 +20,7 @@ def __exit__(self, *args):
 
  def deinitialize(self):
  if self.is_enabled:
+ self.set_period(1)
  self.disable()
  with open(self.SYSFS_PWM_UNEXPORT_PATH, "a") as pwm_unexport:
  pwm_unexport.write(str(self.channel))