[media] af9035: Add possibility to define which I2C adapter to use

Some I2C tuner drivers require that the I2C device of the tuner is added
to the I2C adapter of the demodulator (Si2168+Si2157 for example). Add
possibility to tell af9035_add_i2c_dev which I2C adapter should be used.

Signed-off-by: Olli Salonen <olli.salonen@iki.fi>
Reviewed-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>