x86: truncate ISA addresses to unsigned int

Impact: Cleanup; fix inappropriate macro use

ISA addresses on x86 are mapped 1:1 with the physical address space.
Since the ISA address space is only 24 bits (32 for VLB or LPC) it
will always fit in an unsigned int, and at least in the aha1542 driver
using a wider type would cause an undesirable promotion.  Hence
explicitly cast the ISA bus addresses to unsigned int.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>