r8152: fix the list rx_done may be used without initialization

BugLink: http://bugs.launchpad.net/bugs/1720977

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: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 98d068ab)
Signed-off-by: AceLan Kao <acelan.kao@canonical.com>
Acked-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

drivers/net/usb/r8152.c

@@ -1350,6 +1350,7 @@ 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);