[BugFix] Makes SuperLU::apply(T*, T*) compile again.

Somehow I missed this instance in the transition.

dune/istl/superlu.hh

@@ -643,8 +643,8 @@ namespace Dune
     if(mat.N()+mat.M()==0)
       DUNE_THROW(ISTLError, "Matrix of SuperLU is null!");
 
-    SuperMatrix* mB = B;
-    SuperMatrix* mX = X;
+    SuperMatrix* mB = &B;
+    SuperMatrix* mX = &X;
     SuperMatrix rB, rX;
     if (reusevector) {
       if(first) {

dune/istl/test/superlutest.cc

@@ -78,4 +78,5 @@ int main(int argc, char** argv)
 
   std::cout<<"Defect reduction is "<<res.reduction<<std::endl;
   solver1.apply(x,b, res);
+  solver1.apply(reinterpret_cast<double*>(&x[0]), reinterpret_cast<double*>(&b[0]));
 }