drm/mtk: Use drm_mode_init() for on-stack modes

Initialize on-stack modes with drm_mode_init() to guarantee
no stack garbage in the list head.

Based on the following cocci script, with manual fixups:
@decl@
identifier M;
expression E;
@@
- struct drm_display_mode M = E;
+ struct drm_display_mode M;

@@
identifier decl.M;
expression decl.E;
statement S, S1;
@@
struct drm_display_mode M;
... when != S
+ drm_mode_init(&M, &E);
+
S1

@@
expression decl.E;
@@
- &*E
+ E

Cc: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221107192545.9896-6-ville.syrjala@linux.intel.comReviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/mediatek/mtk_hdmi.c

@@ -1217,7 +1217,7 @@ static int mtk_hdmi_bridge_mode_valid(struct drm_bridge *bridge,
 	if (next_bridge) {
 		struct drm_display_mode adjusted_mode;
 
-		drm_mode_copy(&adjusted_mode, mode);
+		drm_mode_init(&adjusted_mode, mode);
 		if (!drm_bridge_chain_mode_fixup(next_bridge, mode,
 						 &adjusted_mode))
 			return MODE_BAD;