drm/mediatek: add a error return value when clock driver has been prepared

DRM driver get the comp->clk by of_clk_get(), we only
assign NULL to comp->clk when error happened, but do
not return the error number.
Signed-off-by: Bibby Hsieh <bibby.hsieh@mediatek.com>
Signed-off-by: CK Hu <ck.hu@mediatek.com>

drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c

@@ -294,7 +294,7 @@ int mtk_ddp_comp_init(struct device *dev, struct device_node *node,
 	comp->irq = of_irq_get(node, 0);
 	comp->clk = of_clk_get(node, 0);
 	if (IS_ERR(comp->clk))
-		comp->clk = NULL;
+		return PTR_ERR(comp->clk);
 
 	/* Only DMA capable components need the LARB property */
 	comp->larb_dev = NULL;