acer-wmi: Cleanup the failure cleanup handling

Cleanup the failure cleanup handling for brightness and email led.

[cc: Split out from another patch]

Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Carlos Corbacho <carlos@strangeworlds.co.uk>
Signed-off-by: Len Brown <len.brown@intel.com>