uio: add SPDX license tags

For those without any license text present or short reference
to GPL, add SPDX tag.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/uio/uio_netx.c

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * UIO driver for Hilscher NetX based fieldbus cards (cifX, comX).
  * See http://www.hilscher.com for details.
@@ -5,8 +6,6 @@
  * (C) 2007 Hans J. Koch <hjk@hansjkoch.de>
  * (C) 2008 Manuel Traut <manut@linutronix.de>
  *
- * Licensed under GPL version 2 only.
- *
  */
 
 #include <linux/device.h>