drm/i915: don't touch the VDD when disabling the panel

I don't see a reason to touch VDD when we're disabling the panel:
since the panel is enabled, we don't need VDD. This saves a few sleep
calls from the vdd_on and vdd_off functions at every modeset.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=69693
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
[danvet: Fix the patch mangle wiggle has done ... Spotted by Paulo.
Also drop the runtime_pm_put call which now has to go due to different
patch ordering. Also from Paul.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>