leds: lp55xx: add DT bindings for LP55231

The TI55231 appears to be fully compatible to the 5523 model from
National Semicondutor. This patch just adds DT bindings for it.
Signed-off-by: Daniel Mack <zonque@gmail.com>
Acked-by: Milo Kim <milo.kim@ti.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>

Documentation/devicetree/bindings/leds/leds-lp55xx.txt

 Binding for TI/National Semiconductor LP55xx Led Drivers
 
 Required properties:
-- compatible: "national,lp5521" or "national,lp5523" or "ti,lp5562" or "ti,lp8501"
+- compatible: one of
+	national,lp5521
+	national,lp5523
+	ti,lp55231
+	ti,lp5562
+	ti,lp8501
+
 - reg: I2C slave address
 - clock-mode: Input clock mode, (0: automode, 1: internal, 2: external)
 

drivers/leds/leds-lp5523.c

 /*
- * lp5523.c - LP5523 LED Driver
+ * lp5523.c - LP5523, LP55231 LED Driver
  *
  * Copyright (C) 2010 Nokia Corporation
  * Copyright (C) 2012 Texas Instruments
@@ -814,6 +814,7 @@ MODULE_DEVICE_TABLE(i2c, lp5523_id);
 #ifdef CONFIG_OF
 static const struct of_device_id of_lp5523_leds_match[] = {
 	{ .compatible = "national,lp5523", },
+	{ .compatible = "ti,lp55231", },
 	{},
 };