Fix bug injected during skeleton port

This library method originally came from the skeleton project.
While running pep8 after porting it I injected a logic bug.
diff --git a/obmc/dbuslib/bindings.py b/obmc/dbuslib/bindings.py
index 51b9e59..c7da8b8 100644
--- a/obmc/dbuslib/bindings.py
+++ b/obmc/dbuslib/bindings.py
@@ -90,7 +90,7 @@
     @dbus.service.method(
         "org.openbmc.Object.Properties", in_signature='sa{sv}')
     def SetMultiple(self, interface_name, prop_dict):
-        if (interface_name in self.properties):
+        if (interface_name not in self.properties):
             self.properties[interface_name] = {}
 
         value_changed = False