staging: comedi: addi_apci_3501: simplify the PCI bar reading

The board supported by this driver has an eeprom connected to an
AMCC S5933 PCI controller chip. Knowing this, we can simplify the
code that reads the PCI bars to get the iobase addresses used in
the driver.

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>