USB: fix use after free in wacom_sys.c

the following commit added a use after free
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=3D3bea733ab21247290bd552dd6a2cd3049af9adef
Found by coverity (cid #1441)
Signed-off-by: Eric Sesterhenn <snakebyte@gmx.de>
Signed-off-by: "Ping Cheng" <pingc@wacom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/input/wacom_sys.c

@@ -282,8 +282,8 @@ static void wacom_disconnect(struct usb_interface *intf)
 		input_unregister_device(wacom->dev);
 		usb_free_urb(wacom->irq);
 		usb_buffer_free(interface_to_usbdev(intf), 10, wacom->wacom_wac->data, wacom->data_dma);
-		kfree(wacom);
 		kfree(wacom->wacom_wac);
+		kfree(wacom);
 	}
 }