[AMDGPU] Fix DAG types for V_MAD_I64_I32 and V_MAD_U64_U32. NFC. (#123629)

These instructions return a 64-bit result and a 1-bit carry, unlike
smul_lohi and umul_lohi which return a pair of 32-bit results.

This does not appear to make any difference in practice because the DAG
types are not used for anything before these nodes are converted to
MachineInstrs.

Author: jayfoad

llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp

@@ -1045,7 +1045,8 @@ void AMDGPUDAGToDAGISel::SelectMUL_LOHI(SDNode *N) {
   SDValue Zero = CurDAG->getTargetConstant(0, SL, MVT::i64);
   SDValue Clamp = CurDAG->getTargetConstant(0, SL, MVT::i1);
   SDValue Ops[] = {N->getOperand(0), N->getOperand(1), Zero, Clamp};
-  SDNode *Mad = CurDAG->getMachineNode(Opc, SL, N->getVTList(), Ops);
+  SDNode *Mad = CurDAG->getMachineNode(
+      Opc, SL, CurDAG->getVTList(MVT::i64, MVT::i1), Ops);
   if (!SDValue(N, 0).use_empty()) {
     SDValue Sub0 = CurDAG->getTargetConstant(AMDGPU::sub0, SL, MVT::i32);
     SDNode *Lo = CurDAG->getMachineNode(TargetOpcode::EXTRACT_SUBREG, SL,