staging: comedi: adv_pci_dio: remove 'main_pci_region' boardinfo

All the boards use PCI BAR2 for the dev->iobase except for the pci1736
which uses PCI BAR0. Just use the board->cardtype to determine which
PCI BAR to use.

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