media: vicodec: set pixelformat to V4L2_PIX_FMT_FWHT_STATELESS for stateless decoder

for stateless decoder, set the output pixelformat
to V4L2_PIX_FMT_FWHT_STATELESS and the pix info to
pixfmt_stateless_fwht

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>