ACPICA: Allow _WAK method to return an Integer

This can happen if the _WAK method returns nothing (as per ACPI
1.0) but does return an integer if the implicit return mechanism
is enabled.  This is the only method that has this problem,
since it is also defined to return a package of two integers
(ACPI 1.0b+). In all other cases, if a method returns an object
when one was not expected, no warning is issued.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>