hwmon: (nct6775) Avoid using device platform data outside probe function

hwmon: (nct6775) Avoid using device platform data outside probe function

Plan going forward is to attach all device attributes to the hwmon device and no
longer to the platform device. With that change, accessing platform data outside
the probe function will be more difficult. To avoid the problem, change code
to no longer rely on it.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>