virt: Fix crash when introspecting the device

Use the new object_initialize_child() and sysbus_init_child_obj() to
fix the issue.
Signed-off-by: NAlistair Francis <alistair.francis@wdc.com>
Suggested-by: NThomas Huth <thuth@redhat.com>
Reviewed-by: NMichael Clark <mjc@sifive.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>

hw/riscv/virt.c

@@ -274,9 +274,8 @@ static void riscv_virt_board_init(MachineState *machine)
     void *fdt;
 
     /* Initialize SOC */
-    object_initialize(&s->soc, sizeof(s->soc), TYPE_RISCV_HART_ARRAY);
-    object_property_add_child(OBJECT(machine), "soc", OBJECT(&s->soc),
-                              &error_abort);
+    object_initialize_child(OBJECT(machine), "soc", &s->soc, sizeof(s->soc),
+                            TYPE_RISCV_HART_ARRAY, &error_abort, NULL);
     object_property_set_str(OBJECT(&s->soc), VIRT_CPU, "cpu-type",
                             &error_abort);
     object_property_set_int(OBJECT(&s->soc), smp_cpus, "num-harts",