Fix the dropout setting when not initialized in rnn_op. (#28561)

test=develop

paddle/fluid/operators/rnn_op.cu.cc

@@ -89,15 +89,16 @@ class RNNDescriptors {
 
     // ------------------- cudnn dropout descriptors ---------------------
     size_t state_size;
-    if (!is_test_ && !dropout_state->IsInitialized()) {
+    bool is_initialized = dropout_state->IsInitialized();
+    if (!is_test_ && !is_initialized) {
       PADDLE_ENFORCE_CUDA_SUCCESS(
           platform::dynload::cudnnDropoutGetStatesSize(handle, &state_size));
       dropout_state->mutable_data<uint8_t>({static_cast<int64_t>(state_size)},
                                            place);
     }
-    dropout_desc_.descriptor(handle, place, dropout_state->IsInitialized(),
-                             dropout_prob_, is_test_ ? nullptr : dropout_state,
-                             seed_, state_size);
+    dropout_desc_.descriptor(handle, place, is_initialized, dropout_prob_,
+                             is_test_ ? nullptr : dropout_state, seed_,
+                             state_size);
 
 // ------------------- cudnn rnn descriptors ---------------------
 #if CUDNN_VERSION >= 6000