net: lan78xx: fix transfer-buffer memory leak

The interrupt URB transfer-buffer was never freed on disconnect or after
probe errors.

Fixes: 55d7de9d ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 Ethernet device driver")
Cc: Woojung.Huh@microchip.com <Woojung.Huh@microchip.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/lan78xx.c

@@ -3788,6 +3788,7 @@ static int lan78xx_probe(struct usb_interface *intf,
 			usb_fill_int_urb(dev->urb_intr, dev->udev,
 					 dev->pipe_intr, buf, maxp,
 					 intr_complete, dev, period);
+			dev->urb_intr->transfer_flags |= URB_FREE_BUFFER;
 		}
 	}