Fix build of atk0110 with base gcc on i386

[dim]

Summary

Base gcc fails to compile sys/dev/acpi_support/atk0110.c for i386,
with the following -Werror warnings:

cc1: warnings being treated as errors
/usr/src/sys/dev/acpi_support/atk0110.c: In function 'aibs_sysctl':
/usr/src/sys/dev/acpi_support/atk0110.c:456: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
/usr/src/sys/dev/acpi_support/atk0110.c: In function 'aibs_sysctl_ggrp':
/usr/src/sys/dev/acpi_support/atk0110.c:522: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
*** [atk0110.o] Error code 1

This is because on i386, the casts from SYSCTL_HANDLER_ARGS's arg2
(which is an intmax_t) to a pointer reduces the value from 64 bit to
32 bit.

For gcc, this can be fixed by an intermediate cast to intptr_t. Note
that I am assuming the incoming arg2 will always fit into 32 bit!

[dim]

Ping.

[avg]

Oops, I thought I approved this, but apparently it was "only" on IRC.
I hope that your commit message will not contain "assume" and instead will state that we indeed pass a pointer via means of uintmax_t (that must not be narrower than uintptr_t) as we discussed.