hw/cpu/a15mpcore: Fix introspection problem with the a15mpcore_priv device

There is a memory management problem when introspecting the a15mpcore_priv
device. It can be seen with valgrind when running QEMU like this:

echo "{'execute':'qmp_capabilities'} {'execute':'device-list-properties'," \
 "'arguments':{'typename':'a15mpcore_priv'}}"\
 "{'execute': 'human-monitor-command', " \
 "'arguments': {'command-line': 'info qtree'}}"  | \
 valgrind -q aarch64-softmmu/qemu-system-aarch64 -M none,accel=qtest -qmp stdio
{"QMP": {"version": {"qemu": {"micro": 50, "minor": 12, "major": 2},
 "package": "build-all"}, "capabilities": []}}
{"return": {}}
{"return": [{"name": "num-cpu", "type": "uint32"}, {"name": "num-irq",
 "type": "uint32"}, {"name": "a15mp-priv-container[0]", "type":
  "child<qemu:memory-region>"}]}
==24978== Invalid read of size 8
==24978==    at 0x618EBA: qdev_print (qdev-monitor.c:686)
==24978==    by 0x618EBA: qbus_print (qdev-monitor.c:719)
[...]

Use the new sysbus_init_child_obj() function to make sure that we get
the reference counting of the child objects right.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 1531745974-17187-6-git-send-email-thuth@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/cpu/a15mpcore.c

@@ -35,15 +35,13 @@ static void a15mp_priv_initfn(Object *obj)
 {
     SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
     A15MPPrivState *s = A15MPCORE_PRIV(obj);
-    DeviceState *gicdev;
 
     memory_region_init(&s->container, obj, "a15mp-priv-container", 0x8000);
     sysbus_init_mmio(sbd, &s->container);
 
-    object_initialize(&s->gic, sizeof(s->gic), gic_class_name());
-    gicdev = DEVICE(&s->gic);
-    qdev_set_parent_bus(gicdev, sysbus_get_default());
-    qdev_prop_set_uint32(gicdev, "revision", 2);
+    sysbus_init_child_obj(obj, "gic", &s->gic, sizeof(s->gic),
+                          gic_class_name());
+    qdev_prop_set_uint32(DEVICE(&s->gic), "revision", 2);
 }
 
 static void a15mp_priv_realize(DeviceState *dev, Error **errp)