s390x: follow qdev tree to detect SCSI device on a CCW bus

Do not make assumptions on the parent type of the SCSIDevice, instead
use object_dynamic_cast all the way up to the CcwDevice.  This is cleaner
because there is no guarantee that the bus is on a virtio-scsi device;
that is only the case for the default configuration of QEMU's s390x
target.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/s390x/ipl.c

@@ -375,14 +375,18 @@ static CcwDevice *s390_get_ccw_device(DeviceState *dev_st, int *devtype)
                 object_dynamic_cast(OBJECT(dev_st),
                                     TYPE_SCSI_DEVICE);
             if (sd) {
-                SCSIBus *bus = scsi_bus_from_device(sd);
-                VirtIOSCSI *vdev = container_of(bus, VirtIOSCSI, bus);
-                VirtIOSCSICcw *scsi_ccw = container_of(vdev, VirtIOSCSICcw,
-                                                       vdev);
-
-                ccw_dev = (CcwDevice *)object_dynamic_cast(OBJECT(scsi_ccw),
-                                                           TYPE_CCW_DEVICE);
-                tmp_dt = CCW_DEVTYPE_SCSI;
+                SCSIBus *sbus = scsi_bus_from_device(sd);
+                VirtIODevice *vdev = (VirtIODevice *)
+                    object_dynamic_cast(OBJECT(sbus->qbus.parent),
+                                        TYPE_VIRTIO_DEVICE);
+                if (vdev) {
+                    ccw_dev = (CcwDevice *)
+                        object_dynamic_cast(OBJECT(qdev_get_parent_bus(DEVICE(vdev))->parent),
+                                            TYPE_CCW_DEVICE);
+                    if (ccw_dev) {
+                        tmp_dt = CCW_DEVTYPE_SCSI;
+                    }
+                }
             }
         }
     }