staging: comedi: amplc_pci230: shrink struct pci230_board

The `ai_bits`, `ao_bits`, and `min_hwver` members of `struct
pci230_board` are only set to small, non-negative values, so make them
`unsigned char`.  The `have_dio` member is used as a boolean so change
it to a bitfield of type `bool`.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>