Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/drivers/isdn/mISDN/stack.c b/drivers/isdn/mISDN/stack.c
index d97c6dd..27aa329 100644
--- a/drivers/isdn/mISDN/stack.c
+++ b/drivers/isdn/mISDN/stack.c
@@ -1,18 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  *
  * Author	Karsten Keil <kkeil@novell.com>
  *
  * Copyright 2008  by Karsten Keil <kkeil@novell.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
  */
 
 #include <linux/slab.h>
@@ -84,8 +75,7 @@
 			cskb = NULL;
 	}
 	read_unlock(&sl->lock);
-	if (cskb)
-		dev_kfree_skb(cskb);
+	dev_kfree_skb(cskb);
 }
 
 static void
@@ -143,8 +133,7 @@
 	}
 out:
 	mutex_unlock(&st->lmutex);
-	if (skb)
-		dev_kfree_skb(skb);
+	dev_kfree_skb(skb);
 }
 
 static inline int