vfio/fsl-mc: Use the new device life cycle helpers

Also add a comment to mark that vfio core releases device_set if @init
fails.

Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20220921104401.38898-11-kevin.tian@intel.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>