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

With the v4l2_i2c_new_subdev* functions now supporting loading modules
based on modaliases, don't use the module names hardcoded in platform
data by passing a NULL module name to those functions.

The only platform using the VPIF capture device (DM646x EVM) hardcodes
the module names to invalid values (tvp514x-0 and tvp514x-1). As this is
already broken, there's no risk of breaking it more.

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