net: dsa: qca8k: correctly handle mdio read error

[ Upstream commit 6cfc03b ]

Restore original way to handle mdio read error by returning 0xffff.
This was wrongly changed when the internal_mdio_read was introduced,
now that both legacy and internal use the same function, make sure that
they behave the same way.

Fixes: ce062a0 ("net: dsa: qca8k: fix kernel panic with legacy mdio mapping")
Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/net/dsa/qca8k.c

@@ -1287,7 +1287,12 @@ qca8k_internal_mdio_read(struct mii_bus *slave_bus, int phy, int regnum)
 	if (ret >= 0)
 		return ret;
 
-	return qca8k_mdio_read(priv, phy, regnum);
+	ret = qca8k_mdio_read(priv, phy, regnum);
+
+	if (ret < 0)
+		return 0xffff;
+
+	return ret;
 }
 
 static int