gpio: ath79: add MODULE_LICENSE

This fixes the following warning on an allmodconf build:
WARNING: modpost: missing MODULE_LICENSE() in drivers/gpio/gpio-ath79.o

---
 drivers/gpio/gpio-ath79.c | 2 ++
 1 file changed, 2 insertions(+)

index 5fad89dfab7e..f97c32b873b9 100644
@@ -324,3 +324,5 @@ static struct platform_driver ath79_gpio_driver = {
 };
 
 module_platform_driver(ath79_gpio_driver);
+
+MODULE_LICENSE("GPL v2");

2.11.0

I already got some other patch for this but thanks anyway!

Yours,
Linus Walleij