hwmon: (ltc4215) make sysfs file match the alarm cause

The ltc4215 driver used the chip's "power good" status bit to provide
the power1_alarm file. This is wrong: the chip is really reporting the
status of one of the monitored voltages.

Change the sysfs file from power1_alarm to in2_min_alarm instead. This
matches the voltage that the chip is raising an alarm for.

Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>