small error in petsc helpers corrected

AMDiS/src/parallel/PetscHelper.h

@@ -129,9 +129,9 @@ namespace AMDiS
     inline PetscErrorCode options_view(PetscViewer viewer)
     {
 #if (PETSC_VERSION_MINOR >= 7)
-      return PetscOptionsView(PETSC_NULL, PetscViewer);
+      return PetscOptionsView(PETSC_NULL, viewer);
 #else
-      return PetscOptionsView(PetscViewer);
+      return PetscOptionsView(viewer);
 #endif
     }