tiny fix

Author: JiayiFeng

python/paddle/v2/fluid/clip.py

@@ -124,11 +124,11 @@ def init(cls, clip_norm):
 
         cls.global_norm_var = layers.fill_constant(
             shape=[1], dtype="float32", value=0.0)
-        cls.local_norm_var = framework.default_main_program().current_block(
-        ).create_var(
-            name=framework.unique_name("local_norm"),
-            dtype="float32",
-            persistable=False)
+        cls.local_norm_var = framework.default_main_program().block(
+            0).create_var(
+                name=framework.unique_name("local_norm"),
+                dtype="float32",
+                persistable=False)
         cls.clip_norm_var = layers.fill_constant(
             shape=[1], dtype="float32", value=clip_norm)