drm/i915: Avoid use-after-free of intel_encoder in intel_dp_connector_destrpy

The drm_dp_aux is associated with the intel_dp encoder and not the
connector. Since the encoder is destroyed before the connector,
attempting to free the drm_dp_aux from inside the connector cleanup
causes a use-after-free.

This was applied to the patch that CI was happy with, but in the
confusion of so many series trying to make CI happy, the unready
patch was plucked.

Fixes: c191eca1 ("drm/i915: Move intel_connector->unregister to connector->early_unregister")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1466411357-730-1-git-send-email-chris@chris-wilson.co.uk