staging: dgnc: remove error message task

TODO file lists task to remove unnecessary error messages. There are
no unnecessary error messages in the driver, this must have been done
already.

Remove task from TODO file.

Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>