staging: dgnc: remove item from TODO list

TODO file contains task to verify and correct function return
sites. Need to check for and implement correct usage of goto's when
there is work to be done before returning.

Remove task from TODO list after already having completed audit of
directory drivers/staging/dgnc.

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