staging: dgnc: Check sscanf return value

This fixes the following checkpatch.pl warnings:
WARNING: unchecked sscanf return value

Signed-off-by: Roberta Dobrescu <roberta.dobrescu@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>