Fix a GPU bug

Author: JiayiFeng

paddle/fluid/operators/crop_op.h

@@ -39,11 +39,16 @@ static std::vector<int> GetOffsets(const framework::ExecutionContext& ctx) {
     PADDLE_ENFORCE_EQ(
         rank, offsets_tensor->dims()[0],
         "Offsets size should be equal to dimension size of input tensor.");
-    const int* offsets_data = offsets_tensor->data<int>();
-    res.resize(rank);
-    for (size_t i = 0; i < rank; ++i) {
-      res[i] = offsets_data[i];
+    const int* offsets_data;
+    framework::Tensor cpu_tmp_tensor;
+    if (platform::is_cpu_place(offsets_tensor->place())) {
+      offsets_data = offsets_tensor->data<int>();
+    } else {
+      framework::TensorCopySync(*offsets_tensor, platform::CPUPlace(),
+                                &cpu_tmp_tensor);
+      offsets_data = cpu_tmp_tensor.data<int>();
     }
+    res = std::vector<int>(offsets_data, offsets_data + rank);
   } else {
     res = ctx.Attr<std::vector<int>>("offsets");
     PADDLE_ENFORCE_EQ(