(pre-stable) drm/i915: make sure we shut off the panel in eDP configs

BugLink: http://bugs.launchpad.net/bugs/578673

Small modifications needed because of a variable rename.

OriginalAuthor: Jesse Barnes <jbarnes@virtuousgeek.org>
Fix error from the last pull request.  Making sure we shut the panel off
is more correct and saves power.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(backported from commit 5620ae29

 upstream)
Acked-by: Brad Figg <brad.figg@canonical.com>
Acked-by: Steve Conklin <sconklin@canonical.com>
Signed-off-by: Steve Conklin <sconklin@canonical.com>