hwmon: (pwm-fan) Update the duty cycle inorder to control the pwm-fan

pwm_config() must be called with a duty cycle of 0 prior to calling
pwm_disable() to ensure that the pwm signal is set to low.

Reported-by: Markus Reichl <m.reichl@fivetechno.de>
Tested-by: Markus Reichl <m.reichl@fivetechno.de>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
Reviewed-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Signed-off-by: Anand Moon <linux.amoon@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>