title: Error loading CuDNNLSTM with Tensorflow 2.1.0
body: <p>I have:</p>
  
  <pre><code>from keras.layers import Input, LSTM, Dense, TimeDistributed, Activation, BatchNormalization, Dropout, Bidirectional
  from keras.models import Sequential
  from keras.utils import Sequence
  from tensorflow.compat.v1.keras.layers import CuDNNLSTM
  </code></pre>
  
  <p>and</p>
  
  <pre><code>        self.model.add(CuDNNLSTM(lstm1_size, input_shape=(
              seq_length, feature_dim), return_sequences=True))
          # self.model.add(BatchNormalization())
          self.model.add(Dropout(0.2))
          self.model.add(CuDNNLSTM(lstm2_size, return_sequences=True))
          self.model.add(Dropout(0.2))
          self.model.add(CuDNNLSTM(lstm3_size, return_sequences=True))
          self.model.add(Dropout(0.2))
          self.model.add(CuDNNLSTM(lstm4_size, return_sequences=True))
          self.model.add(Dropout(0.2))
          self.model.add(Dense(feature_dim, activation='linear'))
  </code></pre>
  
  <p>But the error I get is:</p>
  
  <pre><code>TypeError: The added layer must be an instance of class Layer. Found: &lt;tensorflow.python.keras.layers.cudnn_recurrent.CuDNNLSTM object at 0x140869be0&gt;
  </code></pre>