PatchToPatchInterpolate: Update to use the tmp ref() non-const access function

Resolves bug-report http://bugs.openfoam.org/view.php?id=2248

src/OpenFOAM/interpolations/patchToPatchInterpolation/PatchToPatchInterpolate.C

@@ -54,7 +54,7 @@ PatchToPatchInterpolation<FromPatch, ToPatch>::pointInterpolate
         new Field<Type>(toPatch_.nPoints(), Zero)
     );
 
-    Field<Type>& result = tresult();
+    Field<Type>& result = tresult.ref();
 
     const List<typename FromPatch::FaceType>& fromPatchLocalFaces =
         fromPatch_.localFaces();
@@ -118,7 +118,7 @@ PatchToPatchInterpolation<FromPatch, ToPatch>::faceInterpolate
         new Field<Type>(toPatch_.size(), Zero)
     );
 
-    Field<Type>& result = tresult();
+    Field<Type>& result = tresult.ref();
 
     const labelListList& fromPatchFaceFaces = fromPatch_.faceFaces();