drm: atmel-hlcdc: fix mode_valid

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
drm: atmel-hlcdc: use drm_connector_unregister/register

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
drm: atmel-hlcdc: output check return code

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
fix mipi dpi