Staging: comedi: usbdux: fix up printk calls

printk() needs a KERN_ level.  But it's usually better to just
use the dev_* functions instead, as they provide much better
information to the user and developer.

Cc: Bernd Porr <BerndPorr@f2s.com>
Cc: David Schleef <ds@schleef.org>
Cc: Frank Mori Hess <fmhess@users.sourceforge.net>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>