acer-wmi: deactive mail led when power off

This patch deactive mail led when laptop is going to hibernete/suspend
or power off. After resume from hibernate/suspend correctly restore
mail led state.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Tested-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>