staging: comedi: usbduxsigma: remove 'probed' checks in comedi functions

The 'probed' flag in the private data is used by the usb_driver (*probe)
function to find a free entry in the static usbduxsub array to use for
the comedi_device private data. The (*probe) sets this flag before it
hands off the probe to the comedi_driver (*auto_attach). The 'probed'
flag is cleared in tidy_up() are part of the usb_driver (*disconnect),
which calls the comedi_driver (*detach).

The 'probed' flag will always be set if the comedi_driver (*auto_attach)
completes successfully. The extra sanity checks in the comedi functions
are not needed. Remove them.

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>