vfio/ccw: Remove private->mdev

There are no remaining users of private->mdev. Remove it.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20220707135737.720765-5-farman@linux.ibm.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>