staging: comedi: addi_apci_16xx: simplify PCI bar reading

The boards supported by this driver do not have an eeprom. Knowing
this information allows simplifying the code that reads the PCI
bars to get the iobase addresses.

The only 'iobase' actually used by this driver is found in PCI
bar 0. Don't bother reading the other PCI bars.

Also, since 'dw_AiBase' is not ioremap'ed we can remove the check
and 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>