staging: comedi: usbduxsigma: tidy up usbduxsub_ao_IsocIrq()

staging: comedi: usbduxsigma: tidy up usbduxsub_ao_IsocIrq()

Rename the local variables to follow the "norm" for comedi drivers.
The comedi_subdevice for this function is the dev->write_subdev that
was initialized during the (*auto_attach), use that instead of
directly accessing the comedi_device subdevices array.

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

Remove the extra check of 'ao_cmd_running' before submitting the urb.
This flag was previously checked and if the command is aborted due to
an usbdux_ao_stop() before reaching this point the function will exit.

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>