net: phy: properly report internal PHYs through sysfs

Internal PHYs may not have a valid PHY interface defined, which will
show up in sysfs as "". Add an explicit check of internal PHYs to report
their interface correctly.

Fixes: 3d055d8d1c24 ("net: phy: expose PHY device interface mode")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/mdio_bus.c

@@ -553,8 +553,14 @@ static ssize_t
 phy_interface_show(struct device *dev, struct device_attribute *attr, char *buf)
 {
 	struct phy_device *phydev = to_phy_device(dev);
+	const char *mode = NULL;
 
-	return sprintf(buf, "%s\n", phy_modes(phydev->interface));
+	if (phy_is_internal(phydev))
+		mode = "internal";
+	else
+		mode = phy_modes(phydev->interface);
+
+	return sprintf(buf, "%s\n", mode);
 }
 static DEVICE_ATTR_RO(phy_interface);