leds: lp55xx: fix the sysfs read operation

According to a sysfs documentation(Documentation/filesystem/sysfs.txt),
scnprintf() should be used in a read operation method.
It guarantees safe buffer size(PAGE_SIZE) which is allocated by the sysfs.
Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>

drivers/leds/leds-lp5521.c

@@ -360,7 +360,8 @@ static ssize_t lp5521_selftest(struct device *dev,
 	mutex_lock(&chip->lock);
 	ret = lp5521_run_selftest(chip, buf);
 	mutex_unlock(&chip->lock);
-	return sprintf(buf, "%s\n", ret ? "FAIL" : "OK");
+
+	return scnprintf(buf, PAGE_SIZE, "%s\n", ret ? "FAIL" : "OK");
 }
 
 /* device attributes */

drivers/leds/leds-lp55xx-common.c

@@ -80,7 +80,7 @@ static ssize_t lp55xx_show_current(struct device *dev,
 {
 	struct lp55xx_led *led = dev_to_lp55xx_led(dev);
 
-	return sprintf(buf, "%d\n", led->led_current);
+	return scnprintf(buf, PAGE_SIZE, "%d\n", led->led_current);
 }
 
 static ssize_t lp55xx_store_current(struct device *dev,
@@ -113,7 +113,7 @@ static ssize_t lp55xx_show_max_current(struct device *dev,
 {
 	struct lp55xx_led *led = dev_to_lp55xx_led(dev);
 
-	return sprintf(buf, "%d\n", led->max_current);
+	return scnprintf(buf, PAGE_SIZE, "%d\n", led->max_current);
 }
 
 static DEVICE_ATTR(led_current, S_IRUGO | S_IWUSR, lp55xx_show_current,