digsig: replace call to kobject_register()

Replace call to removed function kobject_register() with
kobject_init_and_add() in dsi_sysfs.c.

Signed-off-by: Rupert Muchembled <rupert@rmuch.net>
digsig: replace calls to kobject_unregister()

Replace calls to deleted function kobject_unregister() with
kobject_del() in dsi_sysfs.c.

Signed-off-by: Rupert Muchembled <rupert@rmuch.net>