media: staging: tegra-vde: Silence some of checkpatch warnings

Make all strings single line to make them grep'able and add a comment
to the memory barrier.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>