staging: comedi: icp_multi: io_addr is a void __iomem *

The io_addr variable in struct dt3k_private is an ioremap'ed pci
resource and should be void __iomem * not a void *.

This quiets a lot of sparse warings for the writew and readw calls
like:

warning: incorrect type in argument 1 (different address spaces)
   expected void const volatile [noderef] <asn:2>*addr
   got void *<noident>

warning: incorrect type in argument 2 (different address spaces)
   expected void volatile [noderef] <asn:2>*addr
   got void *

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>