media: netup_unidvb: fix use-after-free at del_timer()

When Universal DVB card is detaching, netup_unidvb_dma_fini()
uses del_timer() to stop dma->timeout timer. But when timer
handler netup_unidvb_dma_timeout() is running, del_timer()
could not stop it. As a result, the use-after-free bug could
happen. The process is shown below:

    (cleanup routine)          |        (timer routine)
                               | mod_timer(&dev->tx_sim_timer, ..)
netup_unidvb_finidev()         | (wait a time)
  netup_unidvb_dma_fini()      | netup_unidvb_dma_timeout()
    del_timer(&dma->timeout);  |
                               |   ndev->pci_dev->dev //USE

Fix by changing del_timer() to del_timer_sync().

Link: https://lore.kernel.org/linux-media/20230308125514.4208-1-duoming@zju.edu.cn
Fixes: 52b1eaf4 ("[media] netup_unidvb: NetUP Universal DVB-S/S2/T/T2/C PCI-E card driver")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/pci/netup_unidvb/netup_unidvb_core.c

@@ -697,7 +697,7 @@ static void netup_unidvb_dma_fini(struct netup_unidvb_dev *ndev, int num)
 	netup_unidvb_dma_enable(dma, 0);
 	msleep(50);
 	cancel_work_sync(&dma->work);
-	del_timer(&dma->timeout);
+	del_timer_sync(&dma->timeout);
 }
 
 static int netup_unidvb_dma_setup(struct netup_unidvb_dev *ndev)