!3202 regmap: fix NULL deref on lookup

Merge Pull Request from: @ci-robot 
 
PR sync from: Zhang Zekun <zhangzekun11@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/LWYTKSTM66JYPYQ7GZFKUXVSO3L2GJUT/ 
 
https://gitee.com/openeuler/kernel/issues/I8LTOI 
 
Link:https://gitee.com/openeuler/kernel/pulls/3202

 

Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Reviewed-by: Liu YongQiang <liuyongqiang13@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>