samples/kobject: 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>
Link: https://lore.kernel.org/r/20230208-kobj_type-samples-v1-1-fca804a8e9f3@weissschuh.netSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

samples/kobject/kset-example.c

@@ -185,7 +185,7 @@ ATTRIBUTE_GROUPS(foo_default);
  * release function, and the set of default attributes we want created
  * whenever a kobject of this type is registered with the kernel.
  */
-static struct kobj_type foo_ktype = {
+static const struct kobj_type foo_ktype = {
 	.sysfs_ops = &foo_sysfs_ops,
 	.release = foo_release,
 	.default_groups = foo_default_groups,