leds: leds-ss4200: replace strict_strtoul() with kstrtoul()

The usage of strict_strtoul() is not preferred, because
strict_strtoul() is obsolete. Thus, kstrtoul() should be
used.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>
diff --git a/drivers/leds/leds-ss4200.c b/drivers/leds/leds-ss4200.c
index 57371e1..758c55f 100644
--- a/drivers/leds/leds-ss4200.c
+++ b/drivers/leds/leds-ss4200.c
@@ -459,7 +459,7 @@
 	struct led_classdev *led = dev_get_drvdata(dev);
 	unsigned long blink_state;
 
-	ret = strict_strtoul(buf, 10, &blink_state);
+	ret = kstrtoul(buf, 10, &blink_state);
 	if (ret)
 		return ret;