phy: rockchip-dp: fix return value check in rockchip_dp_phy_probe()

In case of error, the function devm_kzalloc() returns NULL pointer
not ERR_PTR(). The IS_ERR() test in the return value check should
be replaced with NULL test.
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Reviewed-by: NHeiko Stuebner <heiko@sntech.de>
Signed-off-by: NKishon Vijay Abraham I <kishon@ti.com>

drivers/phy/phy-rockchip-dp.c

@@ -90,7 +90,7 @@ static int rockchip_dp_phy_probe(struct platform_device *pdev)
 		return -ENODEV;
 
 	dp = devm_kzalloc(dev, sizeof(*dp), GFP_KERNEL);
-	if (IS_ERR(dp))
+	if (!dp)
 		return -ENOMEM;
 
 	dp->dev = dev;