net: dsa: mv88e6xxx: lock mutex when freeing IRQs

mv88e6xxx_g2_irq_free locks the registers mutex, but not
mv88e6xxx_g1_irq_free, which results in a stack trace from
assert_reg_lock when unloading the mv88e6xxx module. Fix this.

Fixes: 3460a577 ("net: dsa: mv88e6xxx: Mask g1 interrupts and free interrupt")
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -3951,7 +3951,9 @@ static void mv88e6xxx_remove(struct mdio_device *mdiodev)
 	if (chip->irq > 0) {
 		if (chip->info->g2_irqs > 0)
 			mv88e6xxx_g2_irq_free(chip);
+		mutex_lock(&chip->reg_lock);
 		mv88e6xxx_g1_irq_free(chip);
+		mutex_unlock(&chip->reg_lock);
 	}
 }