gpio: ath79: Fix module autoload

If the driver is built as a module, autoload won't work because the module
alias information is not filled. So user-space can't match the registered
device with the corresponding module.

Export the module alias information using the MODULE_DEVICE_TABLE() macro.

Before this patch:

$ modinfo drivers/gpio/gpio-ath79.ko | grep alias
$

After this patch:

$ modinfo drivers/gpio/gpio-ath79.ko | grep alias
alias: of:N*T*Cqca,ar9340-gpioC*
alias: of:N*T*Cqca,ar9340-gpio
alias: of:N*T*Cqca,ar7100-gpioC*
alias: of:N*T*Cqca,ar7100-gpio

Signed-off-by: Javier Martinez Canillas <[e-mail]>
Acked-by: Aban Bedel <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

drivers/gpio/gpio-ath79.c

···
 	{ .compatible = "qca,ar9340-gpio" },
 	{},
 };
+MODULE_DEVICE_TABLE(of, ath79_gpio_of_match);
 
 static int ath79_gpio_probe(struct platform_device *pdev)
 {