[Cleanup] Pass norm by reference

src/one-body-sample.cc

@@ -226,7 +226,7 @@ int main(int argc, char *argv[]) {
     // TODO: clean up once generic lambdas arrive
     auto const solveLinearProblem = [&](
         Dune::BitSetVector<dims> const &_dirichletNodes, Matrix const &_matrix,
-        Vector const &_rhs, Vector &_x, EnergyNorm<Matrix, Vector> _norm,
+        Vector const &_rhs, Vector &_x, EnergyNorm<Matrix, Vector> const &_norm,
         Dune::ParameterTree const &_localParset) {
       LinearFactory factory(parset.sub("solver.tnnmg"), // FIXME
                             refinements, *grid, _dirichletNodes);