[operators.bilinear-form] fix warning

dune/gdt/operators/bilinear-form.hh

@@ -214,10 +214,10 @@ public:
                   "local_source_->size() = " << local_source_->size());
     DUNE_THROW_IF(
         local_range_->size() != 1, Exceptions::bilinear_form_error, "local_range_->size() = " << local_range_->size());
-    for (auto& element_data_ : element_data_) {
-      const auto& local_bilinear_form = *std::get<0>(element_data_);
-      auto& param = std::get<1>(element_data_);
-      const auto& filter = *std::get<2>(element_data_);
+    for (auto& element_data : element_data) {
+      const auto& local_bilinear_form = *std::get<0>(element_data);
+      auto& param = std::get<1>(element_data);
+      const auto& filter = *std::get<2>(element_data);
       if (filter.contains(this->grid_view_, element)) {
         local_bilinear_form.apply2(*local_source_, *local_range_, bilinear_form_value_, param);
         assert(bilinear_form_value_.rows() >= 1);