zonefs: make kobj_type structure 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 definition to prevent
modification at runtime.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>

fs/zonefs/sysfs.c

@@ -79,7 +79,7 @@ static const struct sysfs_ops zonefs_sysfs_attr_ops = {
 	.show	= zonefs_sysfs_attr_show,
 };
 
-static struct kobj_type zonefs_sb_ktype = {
+static const struct kobj_type zonefs_sb_ktype = {
 	.default_groups = zonefs_sysfs_groups,
 	.sysfs_ops	= &zonefs_sysfs_attr_ops,
 	.release	= zonefs_sysfs_sb_release,