media: staging: media: meson: vdec: fix kernel-doc warning

One comment used /** instead of /*, so it caused kernel-doc
warnings. Just turn it into a regular comment.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>