Fix some doc apis example,scale ops

Fix the doc example api for the scale op

python/paddle/fluid/layers/nn.py

@@ -14037,7 +14037,7 @@ def unique(x, dtype='int32'):
 
              import numpy as np
              import paddle.fluid as fluid
-             x = fluid.assign(np.array([2, 3, 3, 1, 5, 3], dtype='int32'))
+             x = fluid.layers.assign(np.array([2, 3, 3, 1, 5, 3], dtype='int32'))
              out, index = fluid.layers.unique(x) # out is [2, 3, 1, 5]; index is [0, 1, 1, 2, 3, 1]
     """