vfio/ap/ccw/samples: Fix device_register() unwind path

vfio/ap/ccw/samples: Fix device_register() unwind path

We always need to call put_device() if device_register() fails.
All vfio drivers calling device_register() include a similar unwind
stack via gotos, therefore split device_unregister() into its
device_del() and put_device() components in the unwind path, and
add a goto target to handle only the put_device() requirement.

Reported-by: Ruan Jinjie <ruanjinjie@huawei.com>
Link: https://lore.kernel.org/all/20221118032827.3725190-1-ruanjinjie@huawei.com
Fixes: d61fc96f47fd ("sample: vfio mdev display - host device")
Fixes: 9d1a546c53b4 ("docs: Sample driver to demonstrate how to use Mediated device framework.")
Fixes: a5e6e6505f38 ("sample: vfio bochs vbe display (host device for bochs-drm)")
Fixes: 9e6f07cd1eaa ("vfio/ccw: create a parent struct")
Fixes: 36360658eb5a ("s390: vfio_ap: link the vfio_ap devices to the vfio_ap bus subsystem")
Cc: Tony Krowiak <akrowiak@linux.ibm.com>
Cc: Halil Pasic <pasic@linux.ibm.com>
Cc: Jason Herne <jjherne@linux.ibm.com>
Cc: Kirti Wankhede <kwankhede@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Tony Krowiak <akrowiak@linux.ibm.com>
Reviewed-by: Jason J. Herne <jjherne@linux.ibm.com>
Link: https://lore.kernel.org/r/166999942139.645727.12439756512449846442.stgit@omen
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>