update some code

Author: wanghaox

paddle/operators/sequence_slice_op.h

@@ -124,14 +124,14 @@ class SequenceSliceGradOpKernel : public framework::OpKernel<T> {
 
     const int64_t* offset_data = offset->data<int64_t>();
     const int64_t* length_data = length->data<int64_t>();
+    framework::Tensor offset_cpu;
+    framework::Tensor length_cpu;
 
     if (platform::is_gpu_place(ctx.GetPlace())) {
-      framework::Tensor offset_cpu;
       offset_cpu.mutable_data<T>(offset->dims(), platform::CPUPlace());
       offset_cpu.CopyFrom(*offset, platform::CPUPlace(), ctx.device_context());
       offset_data = offset_cpu.data<int64_t>();
 
-      framework::Tensor length_cpu;
       length_cpu.mutable_data<T>(length->dims(), platform::CPUPlace());
       length_cpu.CopyFrom(*length, platform::CPUPlace(), ctx.device_context());
       length_data = length_cpu.data<int64_t>();