mtd: use class_groups instead of class_attrs

The class_attrs pointer is long depreciated, and is about to be finally
removed, so move to use the class_groups pointer instead.

Cc: Artem Bityutskiy <[e-mail]>
Acked-by: Richard Weinberger <[e-mail]>
Cc: David Woodhouse <[e-mail]>
Cc: Brian Norris <[e-mail]>
Cc: Boris Brezillon <[e-mail]>
Cc: Marek Vasut <[e-mail]>
Cc: Cyrille Pitchen <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/mtd/ubi/build.c

···
 static DEFINE_SPINLOCK(ubi_devices_lock);
 
 /* "Show" method for files in '/<sysfs>/class/ubi/' */
-static ssize_t ubi_version_show(struct class *class,
-				struct class_attribute *attr, char *buf)
+/* UBI version attribute ('/<sysfs>/class/ubi/version') */
+static ssize_t version_show(struct class *class, struct class_attribute *attr,
+			    char *buf)
 {
 	return sprintf(buf, "%d\n", UBI_VERSION);
 }
+static CLASS_ATTR_RO(version);
 
-/* UBI version attribute ('/<sysfs>/class/ubi/version') */
-static struct class_attribute ubi_class_attrs[] = {
-	__ATTR(version, S_IRUGO, ubi_version_show, NULL),
-	__ATTR_NULL
+static struct attribute *ubi_class_attrs[] = {
+	&class_attr_version.attr,
+	NULL,
 };
+ATTRIBUTE_GROUPS(ubi_class);
 
 /* Root UBI "class" object (corresponds to '/<sysfs>/class/ubi/') */
 struct class ubi_class = {
 	.name		= UBI_NAME_STR,
 	.owner		= THIS_MODULE,
-	.class_attrs	= ubi_class_attrs,
+	.class_groups	= ubi_class_groups,
 };
 
 static ssize_t dev_attribute_show(struct device *dev,