hwmon: (lm90) Export temperature offset values

Now that we have standard sysfs names to export temperature offset
values, add this feature to the lm90 driver. All supported chips
except the MAX6657, MAX6658 and MAX6659 support it.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Hans de Goede <j.w.r.degoede@hhs.nl>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>