drm/panel: simple: Set connector type for DSI panels

None of the DSI panels set the connector_type in their panel_desc
descriptor. As they are all guaranteed to be DSI panels, that's an easy
fix, set the connector type to DRM_MODE_CONNECTOR_DSI.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200602171240.2785-1-laurent.pinchart+renesas@ideasonboard.com