media: dvbdev: fix build warning due to comments

commit 3edfd14b upstream.

Previous commit that introduces reference counter does not add proper
comments, which will lead to warning when building htmldocs. Fix them.

Reported-by: "Stephen Rothwell" <sfr@canb.auug.org.au>
Fixes: 0fc044b2 ("media: dvbdev: adopts refcnt to avoid UAF")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>