Staging: dgnc: Replace printk() with dev_dbg()

This patch replaces printk() with dev_dbg() in order to avoid the
suggestion of using a more specific function while printing debug
information. Warning found by checkpatch.pl.

Signed-off-by: Cristina Opriceana <cristina.opriceana@gmail.com>
Reviewed-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>