drm/i915: Set crtc DPMS mode to ON in intel_crtc_mode_set

This corrects the DPMS mode tracking so that the DPMS code will
actually turn the CRTC off the next time the screen saves.
Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/gpu/drm/i915/intel_display.c

@@ -5273,6 +5273,8 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
 
 	drm_vblank_post_modeset(dev, pipe);
 
+	intel_crtc->dpms_mode = DRM_MODE_DPMS_ON;
+
 	return ret;
 }