V4L/DVB (12343): Stop defining I2C adapter IDs nobody uses

There is no point in defining I2C adapter IDs when no code is using
them. As this field might go away in the future, stop using it when
we don't need to.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>