media: vicodec: add field 'buf' to fwht_raw_frame

Add the field 'buf' to fwht_raw_frame to indicate
the start of the raw frame buffer.
This field will be used to copy the capture buffer
to the reference buffer in the next patch.

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>