Avoid a compiler warning

dune/tnnmg/test/tnnmgsteptest.cc

@@ -61,11 +61,11 @@ void solveProblem(const MatrixType& mat, VectorType& x, const VectorType& rhs, c
     using NonlinearSmoother = Dune::TNNMG::NonlinearGSStep<Functional, decltype(localSolver), BitVector>;
     auto nonlinearSmoother = std::make_shared<NonlinearSmoother>(J, x, localSolver);
 
-    auto smoother = TruncatedBlockGSStep<Matrix, Vector>{};
+    auto smoother = std::make_shared<TruncatedBlockGSStep<Matrix, Vector> >();
 
     auto linearMultigridStep = std::make_shared<Dune::Solvers::MultigridStep<Matrix, Vector> >();
     linearMultigridStep->setMGType(1, 3, 3);
-    linearMultigridStep->setSmoother(&smoother);
+    linearMultigridStep->setSmoother(smoother);
     linearMultigridStep->setTransferOperators(transfer);
 
     using Linearization = Dune::TNNMG::BoxConstrainedQuadraticFunctionalConstrainedLinearization<Functional, BitVector>;