vfio/container: reform vfio_container_connect cleanup

vfio/container: reform vfio_container_connect cleanup

Replace the proliferation of exit labels in vfio_container_connect with
conditionals for cleaning each piece of state.  No functional change.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Cedric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/1746195760-101443-3-git-send-email-steven.sistare@oracle.com
[ clg: vfio_attach_discard_disable() -> vfio_container_attach_discard_disable() ]
Signed-off-by: Cédric Le Goater <clg@redhat.com>