[media] v4l: Remove hardcoded module names passed to v4l2_i2c_new_subdev* (2)

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 in the cafe-ccic, via-camera and s5p-fimc drivers.

All corresponding I2C modules have been checked, and all of them include
a module aliases table with names corresponding to what the drivers
modified here use.

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