media: cedrus: use helper to set default formats

Now that set output format helper is available, let's use that for
setting default values. Advantage of this is that values will be always
valid. Current code produced invalid default values for V3s SoC, which
doesn't support MPEG2 decoding.

Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>