vfio/ccw: Flatten MDEV device (un)register

vfio/ccw: Flatten MDEV device (un)register

The vfio_ccw_mdev_(un)reg routines are merely vfio-ccw routines that
pass control to mdev_(un)register_device. Since there's only one
caller of each, let's just call the mdev routines directly.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Link: https://lore.kernel.org/r/20220707135737.720765-7-farman@linux.ibm.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>