USB: keyspan: fix null-deref at disconnect and release

Make sure to fail properly if the device is not accepted during attach
in order to avoid null-pointer derefs (of missing interface private
data) at disconnect or release.

Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/keyspan.c

@@ -2303,7 +2303,7 @@ static int keyspan_startup(struct usb_serial *serial)
 	if (d_details == NULL) {
 		dev_err(&serial->dev->dev, "%s - unknown product id %x\n",
 		    __func__, le16_to_cpu(serial->dev->descriptor.idProduct));
-		return 1;
+		return -ENODEV;
 	}
 
 	/* Setup private data for serial driver */