[media] rtl2830: add parent for I2C adapter

i2c i2c-6: adapter [RTL2830 tuner I2C adapter] registered
BUG: unable to handle kernel NULL pointer dereference at 0000000000000220
IP: [<ffffffffa0002900>] i2c_register_adapter+0x130/0x390 [i2c_core]

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