Adjust include guard to dune style

dune/solvers/iterationsteps/semidefiniteblockgsstep.hh

-#ifndef SEMIDEFINITEBLOCKGSSTEP_HH
-#define SEMIDEFINITEBLOCKGSSTEP_HH
+#ifndef DUNE_SOLVERS_ITERATIONSTEPS_SEMIDEFINITEBLOCKGSSTEP_HH
+#define DUNE_SOLVERS_ITERATIONSTEPS_SEMIDEFINITEBLOCKGSSTEP_HH
 
 #include <cmath>
 #include <algorithm>
@@ -236,4 +236,4 @@ std::istream& operator>>(std::istream& lhs, typename SemiDefiniteBlockGSStep<M,
 */
 
 
-#endif // SEMIDEFINITEBLOCKGSSTEP_HH
+#endif // DUNE_SOLVERS_ITERATIONSTEPS_SEMIDEFINITEBLOCKGSSTEP_HH