Fix build error in graphics/dri when CPUTYPE is set

[rezny]

Summary

I trimmed the patches a bit too much yesterday and removed a section that looked like the work of sed, but which wasn't or was from a sed command not included in the post-patch, and that removal causes the build to fail when CPUTYPE is set. Add the proper sed magic, courtesy of madpilot, to fix.

Test Plan

Poudriere 11-STABLE amd64 with CPUTYPE set, OK

[swills]

Approved