graphics/drm-current-kmod: Update snapshot

Update graphics/drm-current-kmod to the latest snapshot.
This update takes into account changes in lkpi in base, and makes use of
debugfs in base, instead of the bundled one.

note: If you are on an older version of current, prior to r347973, you might
need to update current first, before updating this driver.

Approved by: jmd (maintainer, implicit)
MFH: 2019Q2 (implicit, drm-driver blanket)
Sponsored by: B3 Init