drm/mediatek: mtk_hdmi_common: Assign DDC adapter pointer to bridge

drm/mediatek: mtk_hdmi_common: Assign DDC adapter pointer to bridge

In preparation for adding the new HDMI TX v2 IP driver, assign the
pointer to the DDC adapter to struct drm_bridge during probe.

This commit brings no functional changes.

Reviewed-by: CK Hu <ck.hu@mediatek.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Louis-Alexis Eyraud <louisalexis.eyraud@collabora.com>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20251023-mediatek-drm-hdmi-v2-v11-6-7873ec4a1edf@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>