!3583 tty: n_gsm: fix the UAF caused by race condition in gsm_cleanup_mux

Merge Pull Request from: @ci-robot 
 
PR sync from: Yi Yang <yiyang13@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/K2QFF37LWGBCVMGE7HTRNKB27KMOY6PF/ 
 
https://gitee.com/src-openeuler/kernel/issues/I8QFUO 
 
Link:https://gitee.com/openeuler/kernel/pulls/3583

 

Reviewed-by: Lu Jialin <lujialin4@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>