[media] rtl2830: carry pointer to I2C client for every function

As a I2C driver struct i2c_client is top level structure representing
the driver. Use it as parameter to carry all needed information for
each function in order to simplify things.
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>