video: use kobj_to_dev()

Use kobj_to_dev() instead of container_of()

Signed-off-by: Wang Qing <wangqing@vivo.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1600776867-24226-1-git-send-email-wangqing@vivo.com