V4L/DVB (9198): adv7170: convert i2c driver for new i2c API

- Convert to use v4l2-i2c-drv-legacy.h to be able to handle the new i2c API
- Cleanups
- Use v4l_dbg/v4l_info to have uniform kernel messages

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>