corrected creator for sequential istl communication

src/amdis/linearalgebra/istl/Communication.inc.hpp

@@ -76,12 +76,12 @@ ISTLCommunication<G,L> CommunicationCreator<ISTLCommunication<G,L>>
 
 #else // HAVE_MPI
 
-template <class Basis>
-std::unique_ptr<ISTLCommunication<Basis>>
-CommunicationCreator<ISTLCommunication<Basis>>
+template <class G, class L>
+  template <class Basis>
+ISTLCommunication<G,L> CommunicationCreator<ISTLCommunication<G,L>>
   ::create(Basis const& /*basis*/, std::string const& /*prefix*/)
 {
-  return std::make_unique<Communication>();
+  return {};
 }
 
 #endif // HAVE_MPI