virtio-scsi: delete vqs in unrealize to avoid memleaks

This patch fix memleaks when attaching/detaching virtio-scsi device, the
memory leak stack is as follow:

Direct leak of 21504 byte(s) in 3 object(s) allocated from:
  #0 0x7f491f2f2970 (/lib64/libasan.so.5+0xef970)  ??:?
  #1 0x7f491e94649d (/lib64/libglib-2.0.so.0+0x5249d)  ??:?
  #2 0x564d0f3919fa (./x86_64-softmmu/qemu-system-x86_64+0x2c3e9fa)  /mnt/sdb/qemu/hw/virtio/virtio.c:2333
  #3 0x564d0f2eca55 (./x86_64-softmmu/qemu-system-x86_64+0x2b99a55)  /mnt/sdb/qemu/hw/scsi/virtio-scsi.c:912
  #4 0x564d0f2ece7b (./x86_64-softmmu/qemu-system-x86_64+0x2b99e7b)  /mnt/sdb/qemu/hw/scsi/virtio-scsi.c:924
  #5 0x564d0f39ee47 (./x86_64-softmmu/qemu-system-x86_64+0x2c4be47)  /mnt/sdb/qemu/hw/virtio/virtio.c:3531
  #6 0x564d0f980224 (./x86_64-softmmu/qemu-system-x86_64+0x322d224)  /mnt/sdb/qemu/hw/core/qdev.c:865

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Pan Nengyuan <pannengyuan@huawei.com>
Message-Id: <20200117075547.60864-2-pannengyuan@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

hw/scsi/virtio-scsi.c

@@ -943,7 +943,13 @@ void virtio_scsi_common_unrealize(DeviceState *dev)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
     VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(dev);
+    int i;
 
+    virtio_del_queue(vdev, 0);
+    virtio_del_queue(vdev, 1);
+    for (i = 0; i < vs->conf.num_queues; i++) {
+        virtio_del_queue(vdev, i + 2);
+    }
     g_free(vs->cmd_vqs);
     virtio_cleanup(vdev);
 }