drm: bridge: Detach all bridges in a chain at encoder cleanup time

Instead of detaching only the bridge directly connected to the encoder,
detach all bridges in the chain.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1481709550-29226-6-git-send-email-laurent.pinchart+renesas@ideasonboard.com