Fix aten-mode copy_tensor_data()

Summary:
I modified this function in D48076575 but got the pointers wrong, causing test failures like https://www.internalfb.com/intern/testinfra/diagnostics/2251800007429278.562950048980124.1691447874/.

Restore the previous logic, which seems to work again.

Reviewed By: larryliu0820

Differential Revision: D48135616

fbshipit-source-id: aa9b22789d82cd20c62a2b3b6a956a5594862a9d

Author: dbort

runtime/core/exec_aten/util/tensor_util_aten.cpp

@@ -58,7 +58,11 @@ Error share_tensor_data(const at::Tensor& t_dst, const at::Tensor& t_src) {
 }
 
 Error copy_tensor_data(const at::Tensor& t_dst, const at::Tensor& t_src) {
-  void* dst_data_ptr = t_dst.mutable_data_ptr();
+  void* dst_data_ptr = t_dst.unsafeGetTensorImpl()
+                           ->unsafe_storage()
+                           .unsafeGetStorageImpl()
+                           ->data_ptr()
+                           .get();
 
   // Currently even 0 sized tensors receive a dataptr in pre_allocated
   // memory planning so we can do this check.