mwifiex: fix NULL pointer dereference in usb suspend handler

Bug 60815 - Interface hangs in mwifiex_usb
https://bugzilla.kernel.org/show_bug.cgi?id=60815

[ 2.883807] BUG: unable to handle kernel NULL pointer dereference
            at 0000000000000048
[ 2.883813] IP: [<ffffffff815a65e0>] pfifo_fast_enqueue+0x90/0x90

[ 2.883834] CPU: 1 PID: 3220 Comm: kworker/u8:90 Not tainted
            3.11.1-monotone-l0 #6
[ 2.883834] Hardware name: Microsoft Corporation Surface with
            Windows 8 Pro/Surface with Windows 8 Pro,
            BIOS 1.03.0450 03/29/2013

On Surface Pro, suspend to ram gives a NULL pointer dereference in
pfifo_fast_enqueue(). The stack trace reveals that the offending
call is clearing carrier in mwifiex_usb suspend handler.

Since commit 1499d9fa "mwifiex: don't drop carrier flag over suspend"
has removed the carrier flag handling over suspend/resume in SDIO
and PCIe drivers, I'm removing it in USB driver too. This also fixes
the bug for Surface Pro.

Cc: <stable@vger.kernel.org> # 3.5+
Tested-by: Dmitry Khromov <icechrome@gmail.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/mwifiex/usb.c

@@ -447,9 +447,6 @@ static int mwifiex_usb_suspend(struct usb_interface *intf, pm_message_t message)
 	 */
 	adapter->is_suspended = true;
 
-	for (i = 0; i < adapter->priv_num; i++)
-		netif_carrier_off(adapter->priv[i]->netdev);
-
 	if (atomic_read(&card->rx_cmd_urb_pending) && card->rx_cmd.urb)
 		usb_kill_urb(card->rx_cmd.urb);
 
@@ -509,10 +506,6 @@ static int mwifiex_usb_resume(struct usb_interface *intf)
 						  MWIFIEX_RX_CMD_BUF_SIZE);
 	}
 
-	for (i = 0; i < adapter->priv_num; i++)
-		if (adapter->priv[i]->media_connected)
-			netif_carrier_on(adapter->priv[i]->netdev);
-
 	/* Disable Host Sleep */
 	if (adapter->hs_activated)
 		mwifiex_cancel_hs(mwifiex_get_priv(adapter,