hwmon: (adm1026) Don't create files for missing inputs

On the ADM1026, pins 27 and 28 can be used for two different functions:
either temp3, or in8+in9. We should only create the sysfs files for the
function that is configured, otherwise it is confusing for the user.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>