drm/panel: panasonic-vvx10f034n00: More return value fixes

A couple more return value fixes which Philippe brought up during our
previous review.
Suggested-by: Philippe CORNU <philippe.cornu@st.com>
Reviewed-by: Philippe Cornu <philippe.cornu@st.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180117213751.54668-1-seanpaul@chromium.org

drivers/gpu/drm/panel/panel-panasonic-vvx10f034n00.c

@@ -59,35 +59,28 @@ static inline struct wuxga_nt_panel *to_wuxga_nt_panel(struct drm_panel *panel)
 
 static int wuxga_nt_panel_on(struct wuxga_nt_panel *wuxga_nt)
 {
-	struct mipi_dsi_device *dsi = wuxga_nt->dsi;
-	int ret;
-
-	ret = mipi_dsi_turn_on_peripheral(dsi);
-	if (ret < 0)
-		return ret;
-
-	return 0;
+	return mipi_dsi_turn_on_peripheral(wuxga_nt->dsi);
 }
 
 static int wuxga_nt_panel_disable(struct drm_panel *panel)
 {
 	struct wuxga_nt_panel *wuxga_nt = to_wuxga_nt_panel(panel);
-	int ret;
+	int mipi_ret, bl_ret = 0;
 
 	if (!wuxga_nt->enabled)
 		return 0;
 
-	ret = mipi_dsi_shutdown_peripheral(wuxga_nt->dsi);
+	mipi_ret = mipi_dsi_shutdown_peripheral(wuxga_nt->dsi);
 
 	if (wuxga_nt->backlight) {
 		wuxga_nt->backlight->props.power = FB_BLANK_POWERDOWN;
 		wuxga_nt->backlight->props.state |= BL_CORE_FBBLANK;
-		backlight_update_status(wuxga_nt->backlight);
+		bl_ret = backlight_update_status(wuxga_nt->backlight);
 	}
 
 	wuxga_nt->enabled = false;
 
-	return ret;
+	return mipi_ret ? mipi_ret : bl_ret;
 }
 
 static int wuxga_nt_panel_unprepare(struct drm_panel *panel)