Fixed __setattr__ method of _MXClassPropertyMetaClass (apache#12811)

* fixed indentation

* simplified code

Author: lostella

python/mxnet/base.py

@@ -165,8 +165,7 @@ def setter(self, func):
 
 class _MXClassPropertyMetaClass(type):
     def __setattr__(cls, key, value):
-        if key in cls.__dict__:
-            obj = cls.__dict__.get(key)
+        obj = cls.__dict__.get(key)
         if obj and isinstance(obj, _MXClassPropertyDescriptor):
             return obj.__set__(cls, value)