[media] i2c: Stop using I2C_CLASS_TV_DIGITAL

Detection class I2C_CLASS_TV_DIGITAL is set by many adapters but no
I2C device driver is setting it anymore, which means it can be
dropped. I2C devices on digital TV adapters are instantiated
explicitly these days, which is much better.

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