drm/bridge: Drop drm_connector_unregister and call drm_connector_cleanup directly

Drop unneeded drm_connector_unregister() and remove the unnecessary
wrapper functions around drm_connector_cleanup().

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161005143133.5549-1-marex@denx.de