graphics/drm-current-kmod: Update messges

Update pkg-message and makefile COMMENT to remove references to
drm-devel-kmod and the mention that this is the development version. It is
the version for FreeBSD CURRENT, so the ride might be a little bumpy, but
it's not the devlopment version.

No changes to package.

FreeBSDDesktop issue: #129

Reported by: grahamperrin
Sponsored by: B3 Init (zeising)