[LegalizeDAG] Use getSignedConstant. NFC

Author: topperc

llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

@@ -1770,7 +1770,7 @@ void SelectionDAGLegalize::ExpandDYNAMIC_STACKALLOC(SDNode* Node,
   Tmp1 = DAG.getNode(Opc, dl, VT, SP, Size);       // Value
   if (Alignment > StackAlign)
     Tmp1 = DAG.getNode(ISD::AND, dl, VT, Tmp1,
-                       DAG.getConstant(-Alignment.value(), dl, VT));
+                       DAG.getSignedConstant(-Alignment.value(), dl, VT));
   Chain = DAG.getCopyToReg(Chain, dl, SPReg, Tmp1);     // Output chain
 
   Tmp2 = DAG.getCALLSEQ_END(Chain, 0, 0, SDValue(), dl);