hwmon: (max6650) Properly support the MAX6650

The MAX6650 has only one fan input.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: "Hans J. Koch" <hjk@hansjkoch.de>
Acked-by: Guenter Roeck <guenter.roeck@ericsson.com>