media: vicodec: keep the ref frame according to the format in decoder

In the decoder, save the inner reference frame in the same
format as the capture buffer.
The decoder writes directly to the capture buffer and then
the capture buffer is copied to the reference buffer.
This will simplify the stateless decoder.

Signed-off-by: Dafna Hirschfeld <dafna3@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>