!5575 net: dsa: fix a crash if ->get_sset_count() fails

Merge Pull Request from: @ci-robot 
 
PR sync from: Ziyang Xuan <william.xuanziyang@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/3TARWGFM7M33LPF5RUQP2ILQU7IV7D4N/ 
 
https://gitee.com/src-openeuler/kernel/issues/I9BHSG 
 
Link:https://gitee.com/openeuler/kernel/pulls/5575

 

Reviewed-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Liu YongQiang <liuyongqiang13@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>