staging: dgnc: Remove all C99 comments

This patch fixes the following checkpatch error:

ERROR: do not use C99 // comments

CC: Lidza Louina <lidza.louina@gmail.com>
Signed-off-by: Seunghun Lee <waydi1@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>