staging: comedi: addi_apci_2200: simplify the PCI bar reading

The board supported by this driver has a 93x76 eeprom. Knowing this
information allows simplifying the code that reads the PCI bars to
get the iobase addresses.

Also, since the 'dw_AiBase' is not ioremap'ed we can remove the iounmap
in the detach.

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