[media] cx231xx: can't proceed if I2C bus register fails

The driver should not ignore errors while registering the I2C
bus, as this device can't even minimally work without the buses,
as it uses those buses internally to talk with the several IP
blocks inside the chip.

Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>