leds: leds-ss4200: Staticize nasgpio_led_get_attr()

nasgpio_led_get_attr() is used only in this file.
Fix the following sparse warning:

drivers/leds/leds-ss4200.c:200:5: warning: symbol 'nasgpio_led_get_attr' was not declared. Should it be static?
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>

drivers/leds/leds-ss4200.c

@@ -197,7 +197,7 @@ static void nasgpio_led_set_attr(struct led_classdev *led_cdev,
 	spin_unlock(&nasgpio_gpio_lock);
 }
 
-u32 nasgpio_led_get_attr(struct led_classdev *led_cdev, u32 port)
+static u32 nasgpio_led_get_attr(struct led_classdev *led_cdev, u32 port)
 {
 	struct nasgpio_led *led = led_classdev_to_nasgpio_led(led_cdev);
 	u32 gpio_in;