The _acpi_module_name was left undefined in these cases, but it
is actually needed as a parameter to some interfaces. Define
_acpi_module_name as a null string in these cases.  Acpica BZ 888.

http://www.acpica.org/bugzilla/show_bug.cgi?id=888Signed-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>