TOMOYO: Add missing poll() hook.

Commit 1dae08c "TOMOYO: Add interactive enforcing mode." forgot to register
poll() hook. As a result, /usr/sbin/tomoyo-queryd was doing busy loop.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>