drm/mediatek: Initialize pointer in mtk_drm_of_ddp_path_build_one()

drm/mediatek: Initialize pointer in mtk_drm_of_ddp_path_build_one()

The struct device_node *next pointer is not initialized, and it is
used in an error path in which it may have never been modified by
function mtk_drm_of_get_ddp_ep_cid().

Since the error path is relying on that pointer being NULL for the
OVL Adaptor and/or invalid component check and since said pointer
is being used in prints for %pOF, in the case that it points to a
bogus address, the print may cause a KP.

To resolve that, initialize the *next pointer to NULL before usage.

Fixes: 4c932840db1d ("drm/mediatek: Implement OF graphs support for display paths")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/dri-devel/633f3c6d-d09f-447c-95f1-dfb4114c50e6@stanley.mountain/
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20241112105030.93337-1-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>