[media] cx18: Don't use module names to load I2C modules

[media] cx18: Don't use module names to load I2C modules

With the v4l2_i2c_new_subdev* functions now supporting loading modules
based on modaliases, replace the hardcoded module name passed to those
functions by NULL.

The sub-devices without a listed module name don't result in and I2C
sub-device being created, as they either are IR devices or don't have an
I2C address listed. It's thus safe to rely on modaliases only.

All corresponding I2C modules have been checked, and all of them include
a module aliases table with names corresponding to what the cx18 driver
uses.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>