Change libxml2 version to 2.9.2
修改libxml2版本为2.9.2

Signed-off-by: 宋万鹏@HP-CQ42 <swpustc@mail.ustc.edu.cn>
update TREE: libxml2 project upgrade
更新TREE：libxml2项目更新

Signed-off-by: 宋万鹏@HP-CQ42 <swpustc@mail.ustc.edu.cn>