[albertagrid] add const qualifier, as we never change the geoInside object

(cherry picked from commit 82682578)
Signed-off-by: Steffen Müthing <muething@dune-project.org>

dune/grid/albertagrid/intersection.cc

@@ -89,7 +89,7 @@ namespace Dune
   inline typename AlbertaGridIntersectionBase< Grid >::NormalVector
   AlbertaGridIntersectionBase< Grid >::centerIntegrationOuterNormal () const
   {
-    typename Entity::Geometry geoInside = inside().geometry();
+    const typename Entity::Geometry geoInside = inside().geometry();
 
     const int face = indexInInside();
     const ReferenceElement< ctype, dimension > &refSimplex = ReferenceElements< ctype, dimension >::simplex();