staging:comedi: Use pr_ or dev_ printks in drivers/usbduxfaxt.c

fixed below checkpatch warnings.
-WARNING: printk() should include KERN_ facility level

Signed-off-by: YAMANE Toshiaki <yamanetoshi@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>