staging: comedi: usbdux: remove dev_printk() noise

Most of these are just function trace noise. The rest report errors
that the user can't do anything about so they amount to added noise.
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>