Unlock before returning on the error path.

Fixes: 5a028e8f ("drm/rockchip: vop2: Add support for rk3588")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240119190841.1619443-1-harshit.m.mogalapalli@oracle.com