exportfs: fix 'passing zero to ERR_PTR()' warning

mainline inclusion
from mainline-4.20-rc5
commit 909e22e0
category: bugfix
bugzilla: 5905
CVE: NA
---------------------------

Fix a static code checker warning:
  fs/exportfs/expfs.c:171 reconnect_one() warn: passing zero to 'ERR_PTR'

The error path for lookup_one_len_unlocked failure
should set err to PTR_ERR.

Fixes: bbf7a8a3 ("exportfs: move most of reconnect_path to helper function")
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NYufen Yu <yuyufen@huawei.com>
Reviewed-by: NHou Tao <houtao1@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/exportfs/expfs.c

@@ -147,6 +147,7 @@ static struct dentry *reconnect_one(struct vfsmount *mnt,
 	tmp = lookup_one_len_unlocked(nbuf, parent, strlen(nbuf));
 	if (IS_ERR(tmp)) {
 		dprintk("%s: lookup failed: %d\n", __func__, PTR_ERR(tmp));
+		err = PTR_ERR(tmp);
 		goto out_err;
 	}
 	if (tmp != dentry) {