ni52: switch to ioremap()

isa_bus_to_virt() is the wrong thing to do here; it happens
to work on i386, but only by accident.  What we want is
normal ioremap/readb/etc. set - it's all in iomem.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jeff Garzik <jeff@garzik.org>