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 <[e-mail]>
Signed-off-by: Bryan Wu <[e-mail]>

drivers/leds/leds-ss4200.c

···
 	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;