During mdev parent registration in mdev_register_device(),
if parent device is duplicate, it releases the reference of existing
parent device.
This is incorrect. Existing parent device should not be touched.

Fixes: 7b96953b ("vfio: Mediated device Core driver")
Reviewed-by: NCornelia Huck <cohuck@redhat.com>
Reviewed-by: NKirti Wankhede <kwankhede@nvidia.com>
Reviewed-by: NMaxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: NParav Pandit <parav@mellanox.com>
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>