usb: xhci-mtk: fix ptr_ret.cocci warnings

drivers/usb/host/xhci-mtk.c:256:1-3: WARNING: PTR_ERR_OR_ZERO can be used

 Use PTR_ERR_OR_ZERO rather than if(IS_ERR(...)) + PTR_ERR

Generated by: scripts/coccinelle/api/ptr_ret.cocci

Fixes: b6bb72cf0df1 ("usb: xhci-mtk: add optional mcu and dma bus clocks")
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Acked-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci-mtk.c

@@ -253,10 +253,7 @@ static int xhci_mtk_clks_get(struct xhci_hcd_mtk *mtk)
 		return PTR_ERR(mtk->mcu_clk);
 
 	mtk->dma_clk = optional_clk_get(dev, "dma_ck");
-	if (IS_ERR(mtk->dma_clk))
-		return PTR_ERR(mtk->dma_clk);
-
-	return 0;
+	return PTR_ERR_OR_ZERO(mtk->dma_clk);
 }
 
 static int xhci_mtk_clks_enable(struct xhci_hcd_mtk *mtk)