media: staging: tegra-vde: Correct minimum size of U/V planes

Stride of U/V planes must be aligned to 16 bytes (2 macroblocks). This
needs to be taken into account, otherwise it is possible to get a silent
memory corruption if dmabuf size is less than the size of decoded video
frame.

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>