[GCC9][Werror]fix -Werror=maybe-uninitialized (#52265)

fix with auto&

paddle/fluid/operators/detection/roi_perspective_transform_op.cc

@@ -256,7 +256,7 @@ class CPUROIPerspectiveTransformOpKernel : public framework::OpKernel<T> {
     auto transformed_width = ctx.Attr<int>("transformed_width");
     auto spatial_scale = ctx.Attr<float>("spatial_scale");
 
-    auto in_dims = in->dims();
+    const auto& in_dims = in->dims();
     int channels = in_dims[1];
     int in_height = in_dims[2];
     int in_width = in_dims[3];