share_pool: Initialize sp_group_master when call k2u_task

ascend inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4EUVI


CVE: NA

-------------------------------------------------

When a process not in any sp group calls k2u_task, it will encounter a
null pointer visit problem in sp_init_proc_stat:

mm->sp_group_master is null, and visit mm->sp_group_master->sp_stat_id
is illegal.

To fix this, we initialize sp_group_master when call k2u_task.

Signed-off-by: Tang Yizhou <tangyizhou@huawei.com>
Reviewed-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: Zhou Guanghui <zhouguanghui1@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>