usbnet: decrease suspend count if returning -EBUSY for runtime suspend

This patch decreases dev->suspend_count in the -EBUSY failure path
of usbnet_suspend. Without the change, the later runtime suspend
will do nothing except for increasing dev->suspend_count.
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Acked-by: NOliver Neukum <oneukum@suse.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/usb/usbnet.c

@@ -1515,6 +1515,7 @@ int usbnet_suspend (struct usb_interface *intf, pm_message_t message)
 		spin_lock_irq(&dev->txq.lock);
 		/* don't autosuspend while transmitting */
 		if (dev->txq.qlen && PMSG_IS_AUTO(message)) {
+			dev->suspend_count--;
 			spin_unlock_irq(&dev->txq.lock);
 			return -EBUSY;
 		} else {