staging: dgnc: Update the TODO file

It turned out that the TODO file contained the invalid information as
some of the work has already been done. This commit updates it with the
current status of what is left to be done.

Signed-off-by: Konrad Zapalowicz <bergo.torino@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>