hwmon: (lm90) Add support for the W83L771W/G

I was wondering if that chip ever existed publicly... Apparently yes,
so add support for it.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Tested-by: Alexander Stein <alexander.stein@informatik.tu-chemnitz.de>
Acked-by: Guenter Roeck <guenter.roeck@ericsson.com>