drm/rockchip: cdn-dp: Don't unregister audio dev when unbinding

After snd_soc_unregister_codec, the dai link would remain bound to
the invalid codec. That would cause crashes after unbind dp driver.

Let's unregister audio codec when removing dp driver to prevent that.

Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1491481885-13775-7-git-send-email-jeffy.chen@rock-chips.com