drm/bridge: ti-sn65dsi86: Get rid of the useless detect() function

If we just leave the detect() function as NULL then the upper layers
assume we're always connected. There's no reason for a stub.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210416153909.v4.6.I826adf4faeb7f39f560b387f6b380e639c6986c8@changeid