scsi: Report error when lun number is in use

In the case that the lun number is taken by another scsi device, don't
release the existing device siliently, but report an error to user.

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/scsi/scsi-bus.c

@@ -177,7 +177,8 @@ static int scsi_qdev_init(DeviceState *qdev)
         d = scsi_device_find(bus, dev->channel, dev->id, dev->lun);
         assert(d);
         if (d->lun == dev->lun && dev != d) {
-            object_unparent(OBJECT(d));
+            error_report("lun already used by '%s'", d->qdev.id);
+            goto err;
         }
     }