drm/imx: imx-ldb: Provide ddc symlink in connector's sysfs

Use the ddc pointer provided by the generic connector.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/bcfe39a0333df951a7d160b3a946c2c32e7eac7f.1564161140.git.andrzej.p@collabora.com