nilfs2: Constify struct kobj_type

'struct kobj_type' is not modified in this driver. It is only used with
kobject_init_and_add() which takes a "const struct kobj_type *" parameter.

Constifying this structure moves some data to a read-only section, so
increase overall security.

On a x86_64, with allmodconfig:
Before:
======
   text	   data	    bss	    dec	    hex	filename
  22403	   4184	     24	  26611	   67f3	fs/nilfs2/sysfs.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  22723	   3928	     24	  26675	   6833	fs/nilfs2/sysfs.o

Link: https://lkml.kernel.org/r/20240708143242.3296-1-konishi.ryusuke@gmail.comSigned-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/nilfs2/sysfs.c

@@ -56,7 +56,7 @@ static void nilfs_##name##_attr_release(struct kobject *kobj) \
 						sg_##name##_kobj); \
 	complete(&subgroups->sg_##name##_kobj_unregister); \
 } \
-static struct kobj_type nilfs_##name##_ktype = { \
+static const struct kobj_type nilfs_##name##_ktype = { \
 	.default_groups	= nilfs_##name##_groups, \
 	.sysfs_ops	= &nilfs_##name##_attr_ops, \
 	.release	= nilfs_##name##_attr_release, \
@@ -166,7 +166,7 @@ static const struct sysfs_ops nilfs_snapshot_attr_ops = {
 	.store	= nilfs_snapshot_attr_store,
 };
 
-static struct kobj_type nilfs_snapshot_ktype = {
+static const struct kobj_type nilfs_snapshot_ktype = {
 	.default_groups	= nilfs_snapshot_groups,
 	.sysfs_ops	= &nilfs_snapshot_attr_ops,
 	.release	= nilfs_snapshot_attr_release,
@@ -967,7 +967,7 @@ static const struct sysfs_ops nilfs_dev_attr_ops = {
 	.store	= nilfs_dev_attr_store,
 };
 
-static struct kobj_type nilfs_dev_ktype = {
+static const struct kobj_type nilfs_dev_ktype = {
 	.default_groups	= nilfs_dev_groups,
 	.sysfs_ops	= &nilfs_dev_attr_ops,
 	.release	= nilfs_dev_attr_release,