hwmon: (w83627ehf) Fix writing into fan_stop_time for NCT6775F/NCT6776F

NCT6775F and NCT6776F have their own set of registers for FAN_STOP_TIME. The
correct registers were used to read FAN_STOP_TIME, but writes used the wrong
registers. Fix it.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Cc: stable@vger.kernel.org # 3.0+
Acked-by: Jean Delvare <khali@linux-fr.org>