hwmon: (lm80) fix checkpatch warnings

fix:
WARNING: simple_strtol is obsolete, use kstrtol instead
WARNING: simple_strtoul is obsolete, use kstrtoul instead

Signed-off-by: Frans Meulenbroeks <fransmeulenbroeks@gmail.com>
[guenter.roeck@ericsson.com: kstrtol->kstrtoul where appropriate]
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>