drm/panel: simple: Add missing panel_simple_unprepare() calls

During panel removal or system shutdown panel_simple_disable() is called
which disables the panel backlight but the panel is still powered due to
missing calls to panel_simple_unprepare().

Fixes: d02fd93e2cd8 ("drm/panel: simple - Disable panel on shutdown")
Cc: stable@vger.kernel.org # v3.16+
Signed-off-by: Jonathan Liu <net147@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170807115545.27747-1-net147@gmail.com

drivers/gpu/drm/panel/panel-simple.c

@@ -370,6 +370,7 @@ static int panel_simple_remove(struct device *dev)
 	drm_panel_remove(&panel->base);
 
 	panel_simple_disable(&panel->base);
+	panel_simple_unprepare(&panel->base);
 
 	if (panel->ddc)
 		put_device(&panel->ddc->dev);
@@ -385,6 +386,7 @@ static void panel_simple_shutdown(struct device *dev)
 	struct panel_simple *panel = dev_get_drvdata(dev);
 
 	panel_simple_disable(&panel->base);
+	panel_simple_unprepare(&panel->base);
 }
 
 static const struct drm_display_mode ampire_am_480272h3tmqw_t01h_mode = {