PPC: [es6] Fix invalid ToString in implementation of ToName.

Port 09626525

R=bmeurer@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, dstence@us.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1377133005

Cr-Commit-Position: refs/heads/master@{#31034}

src/full-codegen/ppc/full-codegen-ppc.cc

@@ -3830,8 +3830,8 @@ void FullCodeGenerator::EmitToName(CallRuntime* expr) {
   __ CompareObjectType(r3, r4, r4, LAST_NAME_TYPE);
   __ ble(&done_convert);
   __ bind(&convert);
-  ToStringStub stub(isolate());
-  __ CallStub(&stub);
+  __ Push(r3);
+  __ CallRuntime(Runtime::kToName, 1);
   __ bind(&done_convert);
   context()->Plug(r3);
 }