hwmon: (nct7802) add temperature sensor type attribute

Sensor type:
3 diode (current mode), MD=1
4 thermistor, MD=2

Reference:
Nuvoton Hardware Monitoring IC NCT7802Y
7.2.32 Mode Selection Register
Location : Index 22h

Signed-off-by: Constantine Shulyupin <const@MakeLinux.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>