emulators/virtualbox-ose-kmod: Fix build with LLVM 15

[jrm]

Summary

When LLVM 15 was imported in 14-CURRENT, the build failed because
starting with clang 15, the -Wint-conversion warning diagnostic for
implicit int <-> pointer conversions defaults to an error. Use a cast to
fix the error.

See also: https://lists.freebsd.org/archives/freebsd-emulation/2023-February/000431.html

https://lists.freebsd.org/archives/freebsd-emulation/2023-February/000460.html

PR: 269721
Reported by: [e-mail], [e-mail], [e-mail]

Test Plan

poudriere build tested on 12/13/14

[lwhsu]

I'm not really on vbox@ but I think this fix is suitable for blanket approval.

[jkim]

FYI, the fix was incomplete. I fixed remaining ones in 7270b8992214.

[jrm]

In D38906#886506, @jkim wrote:

FYI, the fix was incomplete. I fixed remaining ones in 7270b8992214.

Sorry. I didn't see those errors when testing and poudriere testport built fine for me.

http://pkg.ftfl.ca/data/14amd64-default/2023-03-06_16h57m27s/logs/virtualbox-ose-kmod-6.1.36.log