gpio-button-hotplug: use flexible array member

zero length arrays are deprecated.

Fixes coccinelle warning:

WARNING use flexible-array member instead

Signed-off-by: Rosen Penev <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/16848
Signed-off-by: Robert Marko <[email protected]>

package/kernel/gpio-button-hotplug/src/gpio-button-hotplug.c

@@ -302,7 +302,7 @@ struct gpio_keys_button_dev {
 
 	struct device *dev;
 	struct gpio_keys_platform_data *pdata;
-	struct gpio_keys_button_data data[0];
+	struct gpio_keys_button_data data[];
 };
 
 static void gpio_keys_polled_queue_work(struct gpio_keys_button_dev *bdev)