net: sh_eth: fix a missing check of of_get_phy_mode

of_get_phy_mode may fail and return a negative error code;
the fix checks the return value of of_get_phy_mode and
returns NULL of it fails.

Fixes: b356e978 ("sh_eth: add device tree support")
Signed-off-by: Kangjie Lu <kjlu@umn.edu>
Reviewed-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/renesas/sh_eth.c

@@ -3181,12 +3181,16 @@ static struct sh_eth_plat_data *sh_eth_parse_dt(struct device *dev)
 	struct device_node *np = dev->of_node;
 	struct sh_eth_plat_data *pdata;
 	const char *mac_addr;
+	int ret;
 
 	pdata = devm_kzalloc(dev, sizeof(*pdata), GFP_KERNEL);
 	if (!pdata)
 		return NULL;
 
-	pdata->phy_interface = of_get_phy_mode(np);
+	ret = of_get_phy_mode(np);
+	if (ret < 0)
+		return NULL;
+	pdata->phy_interface = ret;
 
 	mac_addr = of_get_mac_address(np);
 	if (mac_addr)