restore tempReg initialization

Author: luke-li-2003

runtime/compiler/p/codegen/J9TreeEvaluator.cpp

@@ -10514,6 +10514,8 @@ hashCodeHelper(TR::Node *node, TR::CodeGenerator *cg, TR::DataType elementType,
    generateTrg1Src2Instruction(cg, TR::InstOpCode::add, node, valueReg, valueReg, endReg);
    generateTrg1Src2Instruction(cg, TR::InstOpCode::add, node, endReg, valueReg, vendReg);
 
+   // initialisations
+   generateTrg1Src2Instruction(cg, TR::InstOpCode::XOR, node, tempReg, tempReg, tempReg);
    loadConstant(cg, node, 0x0, constant0Reg);
 
    // special cases for 0, 1, 2