staging: comedi: addi_apci_1564: use dev->iobase for main registers

According to ADDI-DATA, the PLD Revision 2.x versions of the APCI-1564 use
PCI BAR 0 for the main registers of the board.

Remove the 'amcc_iobase' member of the private data and use the dev->iobase
to store the base address of PCI BAR 1.

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>