[media] cx231xx: give each master i2c bus a seperate name

Instead of using the same name for all 3 i2c physical buses
inside cx231xx, name them differently, adding a number
to it. This helps to better deal with the logs.

[mchehab@osg.samsung.com: removed an unused bus_name var from
 the original patch]
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>