configfs: Constify ct_group_ops in struct config_item_type

Make 'ct_group_ops' const in struct config_item_type.
This allows constification of many structures which hold some function
pointers.

Signed-off-by: Christophe JAILLET <[e-mail]>
Reviewed-by: Breno Leitao <[e-mail]>
Link: https://lore.kernel.org/r/6b720cf407[e-mail]
Signed-off-by: Andreas Hindborg <[e-mail]>

fs/configfs/dir.c

···
 static int populate_attrs(struct config_item *item)
 {
 	const struct config_item_type *t = item->ci_type;
-	struct configfs_group_operations *ops;
+	const struct configfs_group_operations *ops;
 	struct configfs_attribute *attr;
 	struct configfs_bin_attribute *bin_attr;
 	int error = 0;

include/linux/configfs.h

···
 struct config_item_type {
 	struct module				*ct_owner;
 	struct configfs_item_operations		*ct_item_ops;
-	struct configfs_group_operations	*ct_group_ops;
+	const struct configfs_group_operations	*ct_group_ops;
 	struct configfs_attribute		**ct_attrs;
 	struct configfs_bin_attribute		**ct_bin_attrs;
 };