hwmon: (asus_atk0110) Fix upper limit readings

On newer Asus boards the "upper" limit of a sensor is encoded as
delta from the "lower" limit. Fix the driver to correctly handle
this case.

Signed-off-by: Luca Tettamanti <kronos.it@gmail.com>
Tested-by: Alex Macfarlane Smith <nospam@archifishal.co.uk>
Signed-off-by: Jean Delvare <khali@linux-fr.org>