kobject: documentation: Update to refer to kset-example.c.

Signed-off-by: Robert P. J. Day <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/kobject.txt

···
 Example code to copy from
 
 For a more complete example of using ksets and kobjects properly, see the
-sample/kobject/kset-example.c code.
+example programs samples/kobject/{kobject-example.c,kset-example.c},
+which will be built as loadable modules if you select CONFIG_SAMPLE_KOBJECT.