staging: comedi: cb_pcidas64: fix incorrect AI range code handling

The hardware range code values and list of valid ranges for the AI
subdevice is incorrect for several supported boards.  The hardware range
code values for all boards except PCI-DAS4020/12 is determined by
calling `ai_range_bits_6xxx()` based on the maximum voltage of the range
and whether it is bipolar or unipolar, however it only returns the
correct hardware range code for the PCI-DAS60xx boards.  For
PCI-DAS6402/16 (and /12) it returns the wrong code for the unipolar
ranges.  For PCI-DAS64/Mx/16 it returns the wrong code for all the
ranges and the comedi range table is incorrect.

Change `ai_range_bits_6xxx()` to use a look-up table pointed to by new
member `ai_range_codes` of `struct pcidas64_board` to map the comedi
range table indices to the hardware range codes.  Use a new comedi range
table for the PCI-DAS64/Mx/16 boards (and the commented out variants).
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Cc: <stable@vger.kernel.org> # 3.18.x
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>