drm/atmel-hlcdc: Remove redundant call to drm_connector_unregister_all()

drm_connector_unregister_all() is not automatically called by
drm_dev_unregister() so we can drop the local call.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: David Airlie <airlied@linux.ie>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1466501283-19976-2-git-send-email-chris@chris-wilson.co.uk