staging: nvec: cleanup childs on remove

Disable device functions and unregister notifier if available. The
serio device must not be "kzallocated". Otherwise serio_unregister_port
will fail because the device is already freed.

Signed-off-by: Marc Dietrich <marvin24@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>