leds: wm831x: add missing const

Fixed the checkpatch warning as below:

  WARNING: static const char * array should probably be static const char * const

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>
diff --git a/drivers/leds/leds-wm831x-status.c b/drivers/leds/leds-wm831x-status.c
index 74a24cf..6bd5c67 100644
--- a/drivers/leds/leds-wm831x-status.c
+++ b/drivers/leds/leds-wm831x-status.c
@@ -157,7 +157,7 @@
 	return ret;
 }
 
-static const char *led_src_texts[] = {
+static const char * const led_src_texts[] = {
 	"otp",
 	"power",
 	"charger",