drm/bridge: make drm_bridge_funcs const

Make these structures const as they are only stored in the funcs field
of drm_bridge structure, which is of type const.
Done using Coccinelle.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1502207650-20029-1-git-send-email-bhumirks@gmail.com