staging: comedi: addi_apci_1564: store PCI BAR 1 base address in private data

According to ADDI-DATA, only the PLD Revision 2.x versions of the APCI-1564
have the 3 counters. The base address for these counters is found in PCI BAR 1.

For aesthetics, save this base address in the private data. The dev->iobase
can then be used for the main registers of the board.

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>