[media] rtl2830: correct I2C functionality

Implement I2C functionality according to real RTL2830 demod.

Do not send register page in first byte of each I2C write, instead
use logic to set page using own write when needed. Page register is
physical register 0 as generally used.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>