svm: Use vma->vm_pgoff for the nid

ascend inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4DZYE


CVE: NA

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

svm_mmap use the pgoff flag for the security requirement nid, which used
as cdm node.

Signed-off-by: Lijun Fang <fanglijun3@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>