[DAG] SelectionDAG::isSplatValue - early out if binop is not splat. NFCI.

Just return false if we fail to match splats - the remainder of the code is for (fixed)vector operations - shuffles/insertions etc.

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -2483,7 +2483,7 @@ bool SelectionDAG::isSplatValue(SDValue V, const APInt &DemandedElts,
       UndefElts = UndefLHS | UndefRHS;
       return true;
     }
-    break;
+    return false;
   }
   case ISD::ABS:
   case ISD::TRUNCATE: