platform/x86: asus-wmi: Use kobj_to_dev()

Use kobj_to_dev() instead of open-coding it.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: ye xingchen <ye.xingchen@zte.com.cn>
Link: https://lore.kernel.org/r/20220811013203.16010-1-ye.xingchen@zte.com.cn


Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>