Fixed wrong communicator for homogeneous cases.

library/MultiRegions/AssemblyMap/AssemblyMapCG2D.cpp

@@ -505,7 +505,7 @@ namespace Nektar
 
             // Add up hash values if parallel
             int hash = m_hash;
-            m_comm->AllReduce(hash, 
+            m_comm->GetRowComm()->AllReduce(hash, 
                               LibUtilities::ReduceSum);
             m_hash = hash;
         }

library/MultiRegions/AssemblyMap/AssemblyMapCG3D.cpp

@@ -1464,7 +1464,7 @@ namespace Nektar
 
             // Add up hash values if parallel
             int hash = m_hash;
-            m_comm->AllReduce(hash, 
+            m_comm->GetRowComm()->AllReduce(hash, 
                               LibUtilities::ReduceSum);
             m_hash = hash;
         }

library/MultiRegions/AssemblyMap/AssemblyMapDG.cpp

@@ -174,7 +174,7 @@ namespace Nektar
 
             // Add up hash values if parallel
             int hash = m_hash;
-            m_comm->AllReduce(hash, 
+            m_comm->GetRowComm()->AllReduce(hash, 
                               LibUtilities::ReduceSum);
             m_hash = hash;
         }