Initialize output parameter

Or code like this have UB passing uninitialized CmpValue:

```
  int64_t CmpMask, CmpValue;
  if (!TII->analyzeCompare(MI, SrcReg, SrcReg2, CmpMask, CmpValue))
    return false;
  if (TII->optimizeCompareInstr(MI, SrcReg, SrcReg2, CmpMask, CmpValue, MRI)) {
```

Detected by msan with:
-Xclang -enable-noundef-analysis -mllvm -msan-eager-checks=1

Differential Revision: https://reviews.llvm.org/D116831

llvm/lib/Target/Hexagon/HexagonInstrInfo.cpp

@@ -1893,6 +1893,7 @@ bool HexagonInstrInfo::analyzeCompare(const MachineInstr &MI, Register &SrcReg,
     case Hexagon::C4_cmplte:
     case Hexagon::C4_cmplteu:
       SrcReg2 = MI.getOperand(2).getReg();
+      Value = 0;
       return true;
 
     case Hexagon::C2_cmpeqi: