[AArch64] Add indexed check to splitStores. NFC.

Add explicit check for unhandled cases in preparation for delaying
splitStores to post-legalization.

llvm-svn: 305471

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -9366,7 +9366,7 @@ static SDValue splitStores(SDNode *N, TargetLowering::DAGCombinerInfo &DCI,
     return SDValue();
 
   StoreSDNode *S = cast<StoreSDNode>(N);
-  if (S->isVolatile())
+  if (S->isVolatile() || S->isIndexed())
     return SDValue();
 
   SDValue StVal = S->getValue();