staging: comedi: usbduxsigma: generalize the usb_submit_urb functions

Generalize a helper function to replace usbduxsub_submit_{In,Out}URBs().

In the callers, set the 'a[io]_cmd_running' flag after the urbs have been
successfully submitted. This removes the need to clear the flag if the
submit fails.

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>