drm/i915/dp: Flush any outstanding work to turn the VDD off

As we may kick off a delayed workqueue task to switch of the VDD lines, we
need to complete that task prior to turning off the panel (which itself
depends upon VDD being off).

v2: Don't cancel the outstanding work as this may trigger a deadlock

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Keith Packard <keithp@keithp.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_dp.c

@@ -1128,6 +1128,7 @@ static void ironlake_edp_panel_off(struct intel_dp *intel_dp)
 	DRM_DEBUG_KMS("Turn eDP power off\n");
 
 	WARN(intel_dp->want_panel_vdd, "Cannot turn power off while VDD is on\n");
+	ironlake_panel_vdd_off_sync(intel_dp); /* finish any pending work */
 
 	pp = ironlake_get_pp_control(dev_priv);
 	pp &= ~(POWER_TARGET_ON | EDP_FORCE_VDD | PANEL_POWER_RESET | EDP_BLC_ENABLE);