x25_asy: Free x25_asy on x25_asy_open() failure.

Based upon a report by Dmitry Vyukov.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/wan/x25_asy.c

@@ -571,8 +571,10 @@ static int x25_asy_open_tty(struct tty_struct *tty)
 
 	/* Perform the low-level X.25 async init */
 	err = x25_asy_open(sl->dev);
-	if (err)
+	if (err) {
+		x25_asy_free(sl);
 		return err;
+	}
 	/* Done.  We have linked the TTY line to a channel. */
 	return 0;
 }