phy: omap-usb2: Fix missing clk_prepare call when using old dt name

Current code does not call clk_prepare(phy->optclk) when using the old
usb_otg_ss_refclk960m name. Fix it.
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

drivers/phy/phy-omap-usb2.c

@@ -296,10 +296,11 @@ static int omap_usb2_probe(struct platform_device *pdev)
 			dev_warn(&pdev->dev,
 				 "found usb_otg_ss_refclk960m, please fix DTS\n");
 		}
-	} else {
-		clk_prepare(phy->optclk);
 	}
 
+	if (!IS_ERR(phy->optclk))
+		clk_prepare(phy->optclk);
+
 	usb_add_phy_dev(&phy->phy);
 
 	return 0;