!8326  wifi: mac80211: don't return unset power in ieee80211_get_tx_power()

Merge Pull Request from: @ci-robot 
 
PR sync from: Zheng Yejian <zhengyejian1@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/LZUGDELIFKYUCME3VPZ4YU2RDZ4ORDA6/ 
 
https://gitee.com/src-openeuler/kernel/issues/I9RE6D 
 
Link:https://gitee.com/openeuler/kernel/pulls/8326 

Reviewed-by: Yue Haibing <yuehaibing@huawei.com> 
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>