staging: comedi: usbduxsigma: push usb (*probe) into comedi (*auto_attach)

The usb_driver (*probe) already calls comedi_usb_auto_config(), which
will call the comedi_driver (*auto_attach). Move the bulk of the (*probe)
to the (*auto_attach).

This allows the comedi_device private data to be kzalloc'ed and the static
array used to pass the private data from the usb_driver to the comedi_driver
can be removed along with the static semaphore that protected it.

We can also drop a couple variables from the private data since they no
longer are used or needed.

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>