hwmon: (max31790) Clear fan fault after reporting it

Fault bits in MAX31790 are sticky and have to be cleared explicitly.
A write operation into either the 'Target Duty Cycle' register or the
'Target Count' register is necessary to clear a fault.

At the same time, we can never clear cached fault status values before
reading them because the companion fault status for any given fan is
cleared as well when clearing a fault.

Cc: Jan Kundrát <jan.kundrat@cesnet.cz>
Cc: Václav Kubernát <kubernat@cesnet.cz>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Václav Kubernát <kubernat@cesnet.cz>
Link: https://lore.kernel.org/r/20210526154022.3223012-6-linux@roeck-us.net