ext4: make kobj_type structures constant

Since commit ee6d3dd4 ("driver core: make kobj_type constant.")
the driver core allows the usage of const struct kobj_type.

Take advantage of this to constify the structure definitions to prevent
modification at runtime.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230209-kobj_type-ext4-v1-1-6865fb05c1f8@weissschuh.netSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/sysfs.c

@@ -501,13 +501,13 @@ static const struct sysfs_ops ext4_attr_ops = {
 	.store	= ext4_attr_store,
 };
 
-static struct kobj_type ext4_sb_ktype = {
+static const struct kobj_type ext4_sb_ktype = {
 	.default_groups = ext4_groups,
 	.sysfs_ops	= &ext4_attr_ops,
 	.release	= ext4_sb_release,
 };
 
-static struct kobj_type ext4_feat_ktype = {
+static const struct kobj_type ext4_feat_ktype = {
 	.default_groups = ext4_feat_groups,
 	.sysfs_ops	= &ext4_attr_ops,
 	.release	= ext4_feat_release,