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: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
diff --git a/drivers/phy/phy-rockchip-dp.c b/drivers/phy/phy-rockchip-dp.c
index 793ecb6..8b267a7 100644
--- a/drivers/phy/phy-rockchip-dp.c
+++ b/drivers/phy/phy-rockchip-dp.c
@@ -90,7 +90,7 @@
 		return -ENODEV;
 
 	dp = devm_kzalloc(dev, sizeof(*dp), GFP_KERNEL);
-	if (IS_ERR(dp))
+	if (!dp)
 		return -ENOMEM;
 
 	dp->dev = dev;