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: bbf7a8a3562f ("exportfs: move most of reconnect_path to helper function")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
        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) {