Integrity: Pass commname via get_task_comm()

When we pass task->comm to audit_log_untrustedstring(), we need to pass it
via get_task_comm() because task->comm can be changed to contain untrusted
string by other threads after audit_log_untrustedstring() confirmed that
task->comm does not contain untrusted string.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>