r8152: fix the list rx_done may be used without initialization

The list rx_done would be initialized when the linking on occurs.
Therefore, if a napi is scheduled without any linking on before,
the following kernel panic would happen.

	BUG: unable to handle kernel NULL pointer dereference at 000000000000008
	IP: [<ffffffffc085efde>] r8152_poll+0xe1e/0x1210 [r8152]
	PGD 0
	Oops: 0002 [#1] SMP
Signed-off-by: NHayes Wang <hayeswang@realtek.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/usb/r8152.c

@@ -1362,6 +1362,7 @@ static int alloc_all_mem(struct r8152 *tp)
 	spin_lock_init(&tp->rx_lock);
 	spin_lock_init(&tp->tx_lock);
 	INIT_LIST_HEAD(&tp->tx_free);
+	INIT_LIST_HEAD(&tp->rx_done);
 	skb_queue_head_init(&tp->tx_queue);
 	skb_queue_head_init(&tp->rx_queue);