staging: fix comedi NI labpc driver build when ISA_DMA_API is not enabled

Fix ni_labpc.c to build when CONFIG_ISA_DMA_API is not enabled.

This is a driver that supports both ISA and PCI devices.
It now builds when for PCI-only support or for both
ISA and PCI device support.
(It does not support ISA-only without PCI.)

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Frank Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>