usb-bot: Mark device as non hotpluggable

usb-bot creates SCSI bus and immediately makes it
non hotpluggable which was making not possible to
hotplug usb-bot since QEMU would abort at
bus_add_child(scsi-hd) time when usb-bot is
realized.

Mark usb-bot as not hotpluggable so that attempt
to hotplug it would error out even before it gets
to device initialization point.
Signed-off-by: NIgor Mammedov <imammedo@redhat.com>
Signed-off-by: NAndreas Färber <afaerber@suse.de>

hw/usb/dev-storage.c

@@ -770,9 +770,11 @@ static void usb_msd_class_initfn_storage(ObjectClass *klass, void *data)
 static void usb_msd_class_initfn_bot(ObjectClass *klass, void *data)
 {
     USBDeviceClass *uc = USB_DEVICE_CLASS(klass);
+    DeviceClass *dc = DEVICE_CLASS(klass);
 
     uc->realize = usb_msd_realize_bot;
     usb_msd_class_initfn_common(klass);
+    dc->hotpluggable = false;
 }
 
 static const TypeInfo msd_info = {