staging: comedi: adl_pci6208: remove multiple board type support

This driver module now only supports a single board type, so remove the
infrastructure for describing multiple board types.  The comedi
"auto_attach" handler, `pci6208_auto_attach()` doesn't need to set the
comedi device's `board_name` or `board_ptr` members.  The former is
automatically pointed to the comedi driver's `driver_name` by the core
comedi module, and the latter is not used anywhere else.  The AO
subdevice's `n_chans` member can be set to 16 without looking it up in
the single element of `pci6208_boards[]`.  There is no need to pass a
board index from the PCI device table to the "auto_attach" handler.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>