Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/include/linux/iio/driver.h b/include/linux/iio/driver.h
index 7dfb10e..36de60a 100644
--- a/include/linux/iio/driver.h
+++ b/include/linux/iio/driver.h
@@ -1,16 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
 /*
  * Industrial I/O in kernel access map interface.
  *
  * Copyright (c) 2011 Jonathan Cameron
- *
- * 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.
  */
 
 #ifndef _IIO_INKERN_H_
 #define _IIO_INKERN_H_
 
+struct iio_dev;
 struct iio_map;
 
 /**