staging: comedi: usbduxsigma: tidy up firmware upload error messages

Use dev->class_dev for all dev_{level} messages.

Remove the unnecessary error message for a kmemdup() failure.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>