[media] cx231xx: delete i2c_client per bus

For each i2c master there is a i2c_client allocated that could be
deleted now that its only two users have been changed to use their
own i2c_client.

Signed-off-by: Matthias Schwarzott <zzam@gentoo.org>
Reviewed-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>