Description: drm/mediatek: Fix a null pointer crash in mtk_drm_crtc_finish_page_flip
References:
Notes:
 carnil> Introduced in 119f5173628a ("drm/mediatek: Add DRM Driver for Mediatek SoC
 carnil> MT8173."). Vulnerable versions: 4.7-rc1.
Bugs:
upstream: released (6.9-rc1) [c958e86e9cc1b48cac004a6e245154dfba8e163b]
6.8-upstream-stable: released (6.8.2) [3fc88b246a2fc16014e374040fc15af1d3752535]
6.7-upstream-stable: released (6.7.11) [9acee29a38b4d4b70f1f583e5ef9a245db4db710]
6.6-upstream-stable: released (6.6.23) [a3dd12b64ae8373a41a216a0b621df224210860a]
6.1-upstream-stable: released (6.1.83) [d2bd30c710475b2e29288827d2c91f9e6e2b91d7]
5.10-upstream-stable: released (5.10.214) [4688be96d20ffa49d2186523ee84f475f316fd49]
4.19-upstream-stable: released (4.19.311) [accdac6b71d5a2b84040c3d2234f53a60edc398e]
sid: released (6.7.12-1)
6.1-bookworm-security: released (6.1.85-1)
5.10-bullseye-security: needed
4.19-buster-security: needed