!8398 comedi: ni_usb6501: fix NULL-deref in command paths

Merge Pull Request from: @ci-robot 
 
PR sync from: Cui GaoSheng <cuigaosheng1@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/IC5H4AWTHAAJ6XROLRHOIVWJEFC2ICG5/ 
 
https://gitee.com/src-openeuler/kernel/issues/I9RD2V 
 
Link:https://gitee.com/openeuler/kernel/pulls/8398

 

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