hwmon: (asc7621) Bug fixes

* Allow fan minimum RPM to be set to zero without triggering alarms.
* Fix voltage scaling arithmetic and correct scale factors.
* Correct fan1-fan4 alarm bit shifts.
* Correct register address for temp3_smoothing_enable.
* Read the alarm registers with high priority.

Signed-off-by: Ken Milmore <ken.milmore@googlemail.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>