staging: dgnc: Fix warnings relating to printk()

This fixes the following checkpatch.pl warnings:
WARNING: printk() should include KERN_ facility level
It replaces printk() with dev_dbg() in order to avoid the warning that a more
specific function should be used.

Signed-off-by: Roberta Dobrescu <roberta.dobrescu@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>