audit: remove redundant condition check in kauditd_thread()

Warning is found by the code analysis tool:
  "the condition 'if(ac && rc < 0)' is redundant: ac"

The @ac variable has been checked before. It can't be a null pointer
here, so remove the redundant condition check.

Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>