hwmon: (hih6130) Fix missing hih6130->write_length setting

The hih6130->write_length setting was accidently removed by commit
ebc6b9383f3e "hwmon: (hih6130) Convert to devm_hwmon_device_register_with_groups",
fix it.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>