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>
temp[] array needs to have an entry for temp_lcrit

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Update compat.h to improve support of older kernels.

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