staging: comedi: addi_apci_1516: remove devpriv->dw_AiBase

This driver does not ioremap the PCI bar stored in devpriv->dw_AiBase.
Remove the iounmap.

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>