drm/mediatek: Use drm_atomic destroy_state helpers

Use the core destroy_state helpers to destroy core state to ensure we don't
leak if/when more fields get added later.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Bibby Hsieh <bibby.hsieh@mediatek.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1470279597-60453-5-git-send-email-bibby.hsieh@mediatek.com

drivers/gpu/drm/mediatek/mtk_drm_crtc.c

@@ -112,8 +112,7 @@ static void mtk_drm_crtc_reset(struct drm_crtc *crtc)
 	struct mtk_crtc_state *state;
 
 	if (crtc->state) {
-		if (crtc->state->mode_blob)
-			drm_property_unreference_blob(crtc->state->mode_blob);
+		__drm_atomic_helper_crtc_destroy_state(crtc->state);
 
 		state = to_mtk_crtc_state(crtc->state);
 		memset(state, 0, sizeof(*state));

drivers/gpu/drm/mediatek/mtk_drm_plane.c

@@ -73,8 +73,7 @@ static void mtk_plane_reset(struct drm_plane *plane)
 	struct mtk_plane_state *state;
 
 	if (plane->state) {
-		if (plane->state->fb)
-			drm_framebuffer_unreference(plane->state->fb);
+		__drm_atomic_helper_plane_destroy_state(plane->state);
 
 		state = to_mtk_plane_state(plane->state);
 		memset(state, 0, sizeof(*state));