net: dsa: mv88e6xxx: fix SERDES IRQ mapping

The current mv88e6xxx SERDES code checks for negative error code from
irq_find_mapping, while this function returns an unsigned integer. This
patch removes this dead code and simply returns 0 is no IRQ is found.
Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.h

@@ -199,7 +199,7 @@ struct mv88e6xxx_port {
 	u64 vtu_member_violation;
 	u64 vtu_miss_violation;
 	u8 cmode;
-	int serdes_irq;
+	unsigned int serdes_irq;
 };
 
 struct mv88e6xxx_chip {

drivers/net/dsa/mv88e6xxx/serdes.c

@@ -249,11 +249,8 @@ int mv88e6352_serdes_irq_setup(struct mv88e6xxx_chip *chip, int port)
 
 	chip->ports[port].serdes_irq = irq_find_mapping(chip->g2_irq.domain,
 							MV88E6352_SERDES_IRQ);
-	if (chip->ports[port].serdes_irq < 0) {
-		dev_err(chip->dev, "Unable to map SERDES irq: %d\n",
-			chip->ports[port].serdes_irq);
-		return chip->ports[port].serdes_irq;
-	}
+	if (!chip->ports[port].serdes_irq)
+		return 0;
 
 	/* Requesting the IRQ will trigger irq callbacks. So we cannot
 	 * hold the reg_lock.
@@ -690,11 +687,8 @@ int mv88e6390_serdes_irq_setup(struct mv88e6xxx_chip *chip, int port)
 
 	chip->ports[port].serdes_irq = irq_find_mapping(chip->g2_irq.domain,
 							port);
-	if (chip->ports[port].serdes_irq < 0) {
-		dev_err(chip->dev, "Unable to map SERDES irq: %d\n",
-			chip->ports[port].serdes_irq);
-		return chip->ports[port].serdes_irq;
-	}
+	if (!chip->ports[port].serdes_irq)
+		return 0;
 
 	/* Requesting the IRQ will trigger irq callbacks. So we cannot
 	 * hold the reg_lock.