ACPI: WMI: Clean up handling of spec violating data blocks

Acer violate the ACPI-WMI spec by declaring some of their data blocks as
expensive, but with no corresponding WCxx method. There is already some
workaround code in to handle the initial WCxx call (we just ignore a
failure here); but we need to properly check if the second, "clean up",
WCxx call is actually needed or not, rather than fail simply because it
isn't there.

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