_types.py: fix lint errors

Author: abderrahim

src/buildstream/_types.py

@@ -72,11 +72,11 @@ def set_values(mcs, kls, data):
 
         type.__setattr__(kls, "_value_to_entry", value_to_entry)
 
-    def __repr__(self):
-        return "<fastenum '{}'>".format(self.__name__)
+    def __repr__(cls):
+        return "<fastenum '{}'>".format(cls.__name__)
 
-    def __setattr__(self, key, value):
+    def __setattr__(cls, key, value):
         raise AttributeError("Adding new values dynamically is not supported")
 
-    def __iter__(self):
-        return iter(self._value_to_entry.values())
+    def __iter__(cls):
+        return iter(cls._value_to_entry.values())