drm/mediatek: dp: Use devm variant of drm_bridge_add()

drm/mediatek: dp: Use devm variant of drm_bridge_add()

In preparation for adding support for aux-bus, which will add a code
path that may fail after the drm_bridge_add() call, change that to
devm_drm_bridge_add() to simplify failure paths later.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20230725073234.55892-5-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>