"fix comment"

python/paddle/fluid/layers/nn.py

@@ -3051,7 +3051,7 @@ def sequence_pad(x, pad_value, maxlen=None, name=None):
             x = fluid.layers.data(name='y', shape=[10, 5],
                              dtype='float32', lod_level=1)
             pad_value = fluid.layers.assign(
-                input=numpy.array([0], dtype=numpy.float32))
+                input=numpy.array([0.0], dtype=numpy.float32))
             out = fluid.layers.sequence_pad(x=x, pad_value=pad_value)
     """