hwmon: (w83627ehf) Permit enabling SmartFan IV mode if configured at startup

If SmartFan IV mode was configured at startup, it should be possible
to re-enable it later on.

Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Acked-by: Ian Dobson <i.dobson@planet-ian.com>