mfd: wm831x: Use DEVICE_ATTR_RO macro

Use DEVICE_ATTR_RO macro helper instead of plain DEVICE_ATTR, which makes
the code a bit shorter and easier to read.
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/wm831x-otp.c

@@ -38,8 +38,8 @@ static int wm831x_unique_id_read(struct wm831x *wm831x, char *id)
 	return 0;
 }
 
-static ssize_t wm831x_unique_id_show(struct device *dev,
-				     struct device_attribute *attr, char *buf)
+static ssize_t unique_id_show(struct device *dev,
+			      struct device_attribute *attr, char *buf)
 {
 	struct wm831x *wm831x = dev_get_drvdata(dev);
 	int rval;
@@ -52,7 +52,7 @@ static ssize_t wm831x_unique_id_show(struct device *dev,
 	return sprintf(buf, "%*phN\n", WM831X_UNIQUE_ID_LEN, id);
 }
 
-static DEVICE_ATTR(unique_id, 0444, wm831x_unique_id_show, NULL);
+static DEVICE_ATTR_RO(unique_id);
 
 int wm831x_otp_init(struct wm831x *wm831x)
 {