staging: comedi: daqboard2000: void *plx should be a void __iomem *

The private data variable 'plx' is an ioremap'ed pci resource and
should be a void __iomem *. This quiets a number of sparse warnings
about "different address spaces".

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>