ovl: do not fail because of O_NOATIME

mainline inclusion
from mainline-v5.11-rc1
commit b6650dab
category: bugfix
bugzilla: NA
CVE: CVE-2020-16120

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

In case the file cannot be opened with O_NOATIME because of lack of
capabilities, then clear O_NOATIME instead of failing.

Remove WARN_ON(), since it would now trigger if O_NOATIME was cleared.
Noticed by Amir Goldstein.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>