hwmon: (lm78) Prevent misdetection of Winbond chips

The LM78 detection is relatively weak, and sometimes recent Winbond
chips can be misdetected as an LM78. We have had repeated reports of
this happening. We have an explicit check against this for the ISA
access, do the same for I2C access now.

Signed-off-by: Jean Delvare <khali@linux-fr.org>