drm/mediatek: Fix potential NULL dereference in mtk_crtc_destroy()

mainline inclusion
from mainline-v6.12-rc6
commit 4018651ba5c409034149f297d3dd3328b91561fd
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IB5KR0
CVE: CVE-2024-53056

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4018651ba5c409034149f297d3dd3328b91561fd



--------------------------------

In mtk_crtc_create(), if the call to mbox_request_channel() fails then we
set the "mtk_crtc->cmdq_client.chan" pointer to NULL.  In that situation,
we do not call cmdq_pkt_create().

During the cleanup, we need to check if the "mtk_crtc->cmdq_client.chan"
is NULL first before calling cmdq_pkt_destroy().  Calling
cmdq_pkt_destroy() is unnecessary if we didn't call cmdq_pkt_create() and
it will result in a NULL pointer dereference.

Fixes: 7627122f ("drm/mediatek: Add cmdq_handle in mtk_crtc")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/cc537bd6-837f-4c85-a37b-1a007e268310@stanley.mountain/


Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

Conflicts:
	drivers/gpu/drm/mediatek/mtk_crtc.c
	drivers/gpu/drm/mediatek/mtk_drm_crtc.c
[Ma Wupeng: file and function has been renamed, no real changes]
Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>