staging: comedi: usbduxsigma: tidy up usbduxsub_submit_PwmURBs()

Rename the CamelCase function.

Pass the comedi_device pointer instead of the private data pointer
to the function.

Use a couple local variables to tidy up the function.

Remove the dev_err() message when usb_submit_urb() fails, its just
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>