[es6] Fix prototype chain walk for instanceof.

src/crankshaft/s390/lithium-codegen-s390.cc

Index: src/crankshaft/s390/lithium-codegen-s390.cc
diff --git a/src/crankshaft/s390/lithium-codegen-s390.cc b/src/crankshaft/s390/lithium-codegen-s390.cc
index 2950d96a7edb1e051ef6420696048e7ff6e9299f..6a409983423c881a1b45504581dcc41ec673a583 100644
--- a/src/crankshaft/s390/lithium-codegen-s390.cc
+++ b/src/crankshaft/s390/lithium-codegen-s390.cc
@@ -2568,10 +2568,10 @@ void LCodeGen::DoHasInPrototypeChainAndBranch(
   DeoptimizeIf(eq, instr, Deoptimizer::kProxy);
   __ LoadP(object_prototype,
            FieldMemOperand(object_map, Map::kPrototypeOffset));
-  __ CmpP(object_prototype, prototype);
-  EmitTrueBranch(instr, eq);
   __ CompareRoot(object_prototype, Heap::kNullValueRootIndex);
   EmitFalseBranch(instr, eq);
+  __ CmpP(object_prototype, prototype);
+  EmitTrueBranch(instr, eq);
   __ LoadP(object_map,
            FieldMemOperand(object_prototype, HeapObject::kMapOffset));
   __ b(&loop);