ITE drivers/pwm/it8xxx2: don't gate pwm clock when set cycle

When pwm_it8xxx2_set_cycles() is called, we disable the pwm clock
at the beginning and enable it at the end, so there is a more than
1ms pwm low pulse when every time changing the cycle. The low pulse
would let some fans go to idle mode, so we don't gate the pwm clock.

Signed-off-by: Ruibin Chang <Ruibin.Chang@ite.com.tw>