watchdog: gxp: Add missing MODULE_LICENSE

The build system says:

ERROR: modpost: missing MODULE_LICENSE() in drivers/watchdog/gxp-wdt.o

Add the missing MODULE_LICENSE.
Signed-off-by: Nick Hawkins <nick.hawkins@hpe.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/all/20220603131419.2948578-1-linux@roeck-us.net/Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/gxp-wdt.c

@@ -172,3 +172,4 @@ module_platform_driver(gxp_wdt_driver);
 MODULE_AUTHOR("Nick Hawkins <nick.hawkins@hpe.com>");
 MODULE_AUTHOR("Jean-Marie Verdun <verdun@hpe.com>");
 MODULE_DESCRIPTION("Driver for GXP watchdog timer");
+MODULE_LICENSE("GPL");