net: dsa: mv88e6xxx: check errors in mv88e6352_serdes_irq_link

The mv88e6352_serdes_irq_link helper is not checking for any error that
may occur during hardware accesses. Worst, the "up" boolean is set from
the potentially unused "status" variable, if read operations failed.

As done in mv88e6390_serdes_irq_link_sgmii, return right away and do
not call dsa_port_phylink_mac_change if an error occurred.
Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/serdes.c

@@ -186,14 +186,19 @@ static void mv88e6352_serdes_irq_link(struct mv88e6xxx_chip *chip, int port)
 	struct dsa_switch *ds = chip->ds;
 	u16 status;
 	bool up;
+	int err;
 
-	mv88e6352_serdes_read(chip, MII_BMSR, &status);
+	err = mv88e6352_serdes_read(chip, MII_BMSR, &status);
+	if (err)
+		return;
 
 	/* Status must be read twice in order to give the current link
 	 * status. Otherwise the change in link status since the last
 	 * read of the register is returned.
 	 */
-	mv88e6352_serdes_read(chip, MII_BMSR, &status);
+	err = mv88e6352_serdes_read(chip, MII_BMSR, &status);
+	if (err)
+		return;
 
 	up = status & BMSR_LSTATUS;