hw/s390x/s390-stattrib: Don't call register_savevm_live() during instance_init()

hw/s390x/s390-stattrib: Don't call register_savevm_live() during instance_init()

We must not call register_savevm_live() from an instance_init() function
(since this could be called multiple times during device introspection).
Move this to the realize() function instead.

Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <20231020150554.664422-4-thuth@redhat.com>