hwmon: (it87) Don't configure 16 bit fan counters it not necessary

On IT8728F, IT8771E, and IT8772E, fans counters are always 16 bit
and don't need to be configured for it.

Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>