hw/isa: Realize ISA bridge device before accessing it

qbus_new() should not be called on unrealized device.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20231019071611.98885-9-philmd@linaro.org>

hw/isa/isa-bus.c

@@ -52,18 +52,25 @@ static const TypeInfo isa_bus_info = {
 ISABus *isa_bus_new(DeviceState *dev, MemoryRegion* address_space,
                     MemoryRegion *address_space_io, Error **errp)
 {
+    DeviceState *bridge = NULL;
+
     if (isabus) {
         error_setg(errp, "Can't create a second ISA bus");
         return NULL;
     }
     if (!dev) {
-        dev = qdev_new("isabus-bridge");
-        sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), &error_fatal);
+        bridge = qdev_new("isabus-bridge");
+        dev = bridge;
     }
 
     isabus = ISA_BUS(qbus_new(TYPE_ISA_BUS, dev, NULL));
     isabus->address_space = address_space;
     isabus->address_space_io = address_space_io;
+
+    if (bridge) {
+        sysbus_realize_and_unref(SYS_BUS_DEVICE(bridge), &error_fatal);
+    }
+
     return isabus;
 }