oeqa/core/decorator/__init__.py: use 'cls' instead of 'obj'

Use 'cls' instead of 'obj' to better reflect that registerDecorator
actually serves as a class decorator.

(From OE-Core rev: e06e4c859e8be5225d80806a2ebe175f0b152fe1)

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/core/decorator/__init__.py

@@ -6,9 +6,9 @@ from abc import abstractmethod, ABCMeta
 
 decoratorClasses = set()
 
-def registerDecorator(obj):
-    decoratorClasses.add(obj)
-    return obj
+def registerDecorator(cls):
+    decoratorClasses.add(cls)
+    return cls
 
 class OETestDecorator(object, metaclass=ABCMeta):
     case = None # Reference of OETestCase decorated