mfd: sm501: 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>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/sm501.c

@@ -1190,13 +1190,13 @@ static int sm501_register_gpio_i2c(struct sm501_devdata *sm,
 	return 0;
 }
 
-/* sm501_dbg_regs
+/* dbg_regs_show
  *
  * Debug attribute to attach to parent device to show core registers
 */
 
-static ssize_t sm501_dbg_regs(struct device *dev,
-			      struct device_attribute *attr, char *buff)
+static ssize_t dbg_regs_show(struct device *dev,
+			     struct device_attribute *attr, char *buff)
 {
 	struct sm501_devdata *sm = dev_get_drvdata(dev)	;
 	unsigned int reg;
@@ -1213,7 +1213,7 @@ static ssize_t sm501_dbg_regs(struct device *dev,
 }
 
 
-static DEVICE_ATTR(dbg_regs, 0444, sm501_dbg_regs, NULL);
+static DEVICE_ATTR_RO(dbg_regs);
 
 /* sm501_init_reg
  *