[media] saa7164: change Si2168 reglen to 0 bit

The i2c_reg_len for Si2168 should be 0 for correct I2C communication.

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>