hwmon: (adm1031) Replace update_rate sysfs attribute with update_interval

The attribute reflects an interval, not a rate.

Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Acked-by: Ira W. Snyder <iws@ovro.caltech.edu>
Signed-off-by: Jean Delvare <khali@linux-fr.org>