[cc][fvelemgeom] make numScv() constexpr

dumux/discretization/cellcentered/mpfa/fvelementgeometry.hh

@@ -126,10 +126,10 @@ public:
                                                  ScvfIterator(g.scvfIndicesOfScv(scvIdx).end(), fvGeometry));
     }
 
-    //! number of sub control volumes in this fv element geometry
-    std::size_t numScv() const
+    //! number of sub control volumes in this fv element geometry (always one for cc schemes)
+    static constexpr std::size_t numScv()
     {
-        return scvIndices_.size();
+        return 1;
     }
 
     //! number of sub control volumes in this fv element geometry
@@ -247,9 +247,9 @@ public:
         return Dune::IteratorRange<IteratorType>(g.scvfs_.begin(), g.scvfs_.end());
     }
 
-    //! number of sub control volumes in this fv element geometry
-    std::size_t numScv() const
-    { return scvs_.size(); }
+    //! number of sub control volumes in this fv element geometry (always one for cc schemes)
+    static constexpr std::size_t numScv()
+    { return 1; }
 
     //! number of sub control volumes in this fv element geometry
     std::size_t numScvf() const