fix flatten api grad (#30426)

paddle/fluid/operators/flatten_op.h

@@ -68,7 +68,9 @@ class FlattenGradKernel : public framework::OpKernel<T> {
     auto in_dims = ctx.Input<framework::LoDTensor>("X")->dims();
 
     d_x->mutable_data(ctx.GetPlace(), d_out->type());
-    framework::TensorCopySync(*d_out, ctx.GetPlace(), d_x);
+    framework::TensorCopy(
+        *d_out, ctx.GetPlace(),
+        ctx.template device_context<platform::DeviceContext>(), d_x);
     d_x->Resize(in_dims);
   }
 };
@@ -107,7 +109,9 @@ class Flatten2GradKernel : public framework::OpKernel<T> {
     auto x_dims = framework::slice_ddim(xshape_dims, 1, xshape_dims.size());
 
     d_x->mutable_data(ctx.GetPlace(), d_out->type());
-    framework::TensorCopySync(*d_out, ctx.GetPlace(), d_x);
+    framework::TensorCopy(
+        *d_out, ctx.GetPlace(),
+        ctx.template device_context<platform::DeviceContext>(), d_x);
     d_x->Resize(x_dims);
   }
 };
@@ -175,7 +179,9 @@ class FlattenContiguousRangeGradKernel : public framework::OpKernel<T> {
     auto x_dims = framework::slice_ddim(xshape_dims, 1, xshape_dims.size());
 
     d_x->mutable_data(ctx.GetPlace(), d_out->type());
-    framework::TensorCopySync(*d_out, ctx.GetPlace(), d_x);
+    framework::TensorCopy(
+        *d_out, ctx.GetPlace(),
+        ctx.template device_context<platform::DeviceContext>(), d_x);
     d_x->Resize(x_dims);
   }
 };