linuxkpi: Correct DIV_ROUND_DOWN_ULL

This fixes a black screen issue with the i915 DRM driver from Linux v6.8

Fixes: c4e0746e7d5bd ("LinuxKPI: Add helper macros IS_ALIGNED and DIV_ROUND_DOWN_ULL.")
Pull request: https://github.com/freebsd/freebsd-src/pull/1612