Fix build of si with base gcc on i386

[dim]

Summary

Base gcc fails to compile sys/dev/si/si_isa.c and
sys/dev/si/si_pci.c for i386, with the following -Werror warnings:

cc1: warnings being treated as errors
/usr/src/sys/modules/si/../../dev/si/si_isa.c: In function 'si_isa_probe':
/usr/src/sys/modules/si/../../dev/si/si_isa.c:68: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
/usr/src/sys/modules/si/../../dev/si/si_isa.c: In function 'si_isa_attach':
/usr/src/sys/modules/si/../../dev/si/si_isa.c:282: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]

cc1: warnings being treated as errors
/usr/src/sys/modules/si/../../dev/si/si_pci.c: In function 'si_pci_attach':
/usr/src/sys/modules/si/../../dev/si/si_pci.c:89: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]

This is because on i386, the casts from rman_res_t (aka uintmax_t)
to a pointer reduces the value from 64 bit to 32 bit.

For gcc, this can be fixed by an intermediate cast to uintptr_t. Note
that I am assuming the incoming values will always fit into 32 bit!

[dim]

Btw, this will be a direct commit to stable/11, since si was removed from head.

[jhb]

Ok I guess. This driver was a dumpster fire. I had patches to fix things like this but no one tested them. This bandaid is probably fine.