hw/ppc: Use object_initialize_child for correct reference counting

hw/ppc: Use object_initialize_child for correct reference counting

Both functions, object_initialize() and object_property_add_child() increase
the reference counter of the new object, so one of the references has to be
dropped afterwards to get the reference counting right. Otherwise the child
object will not be properly cleaned up when the parent gets destroyed.
Thus let's use now object_initialize_child() instead to get the reference
counting here right.

Suggested-by: Eduardo Habkost <[email protected]>
Signed-off-by: Thomas Huth <[email protected]>
Message-Id: <1550748288[email protected]>
Reviewed-by: Cédric Le Goater <[email protected]>
Signed-off-by: David Gibson <[email protected]>