Fix context register allocation in LTransitionElementsKind.

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index 78bc5bb7089322c6e93a574b137ceb53d0f72e08..eb005931a272cd6a7b27c2a5de313b63ae6483ff 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -2266,7 +2266,7 @@ LInstruction* LChunkBuilder::DoTransitionElementsKind(
         object, NULL, new_map_reg, temp_reg);
     return result;
   } else {
-    LOperand* context = UseAny(instr->context());
+    LOperand* context = UseFixed(instr->context(), rsi);
     LTransitionElementsKind* result =
         new(zone()) LTransitionElementsKind(object, context, NULL, NULL);
     return AssignPointerMap(result);