ACPI: remove NID_INVAL

b552a8c5 ("ACPI: remove NID_INVAL") removed the left over uses of
NID_INVAL, but didn't actually remove the definition.  Remove it.

Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>