PPC: VectorICs: megamorphic keyed loads in crankshaft don't need a vector.

Port c8e4d57d

Original commit message:
They are content with a dummy vector, as MISSES won't result in
changing the real vector/slot at all.

R=mvstanton@chromium.org, michael_dawson@ca.ibm.com, dstence@us.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1085913003

Cr-Commit-Position: refs/heads/master@{#27850}

src/ppc/lithium-codegen-ppc.cc

@@ -3543,7 +3543,7 @@ void LCodeGen::DoLoadKeyedGeneric(LLoadKeyedGeneric* instr) {
   DCHECK(ToRegister(instr->object()).is(LoadDescriptor::ReceiverRegister()));
   DCHECK(ToRegister(instr->key()).is(LoadDescriptor::NameRegister()));
 
-  if (FLAG_vector_ics) {
+  if (instr->hydrogen()->HasVectorAndSlot()) {
     EmitVectorLoadICRegisters<LLoadKeyedGeneric>(instr);
   }