mfd: Replace strict_strtoul() with kstrtoul() in ab* and att*

The usage of strict_strtoul() is not preferred, because
strict_strtoul() is obsolete. Thus, kstrtoul() should be
used.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/aat2870-core.c

@@ -312,8 +312,9 @@ static ssize_t aat2870_reg_write_file(struct file *file,
 	while (*start == ' ')
 		start++;
 
-	if (strict_strtoul(start, 16, &val))
-		return -EINVAL;
+	ret = kstrtoul(start, 16, &val);
+	if (ret)
+		return ret;
 
 	ret = aat2870->write(aat2870, (u8)addr, (u8)val);
 	if (ret)