ascend inclusion
category: feature
bugzilla: NA
CVE: NA

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

DVPP process channel destroy procedure:
do_exit() -> exit_mm() (mm no longer in spg) -> exit_task_work()
-> task_work_run() -> __fput() -> ... -> vdec_close() ->
sp_unshare(uva, ..., SPG_ID_DEFAULT).

So when it calls sp_unshare(), current->mm is NULL, just like
buff_module_guard_work kthread.

To solve this problem, we skip corresponding sanity checks.
Signed-off-by: NTang Yizhou <tangyizhou@huawei.com>
Reviewed-by: NDing Tianhong <dingtianhong@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>