irq_find_mapping() returns a positive IRQ number or 0 if no IRQ is found
but it never returns a negative value. However, during the PTP IRQ setup,
we verify that its returned value isn't negative.

Fix the irq_find_mapping() check to enter the error path when 0 is
returned. Return -EINVAL in such case.

Fixes: cc13ab18b201 ("net: dsa: microchip: ptp: enable interrupt for timestamping")
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Bastien Curutchet (Schneider Electric) <bastien.curutchet@bootlin.com>
---
 drivers/net/dsa/microchip/ksz_ptp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/dsa/microchip/ksz_ptp.c b/drivers/net/dsa/microchip/ksz_ptp.c
index 35fc21b1ee48a47daa278573bfe8749c7b42c731..c8bfbe5e2157323ecf29149d1907b77e689aa221 100644
--- a/drivers/net/dsa/microchip/ksz_ptp.c
+++ b/drivers/net/dsa/microchip/ksz_ptp.c
@@ -1139,8 +1139,8 @@ int ksz_ptp_irq_setup(struct dsa_switch *ds, u8 p)
 		irq_create_mapping(ptpirq->domain, irq);
 
 	ptpirq->irq_num = irq_find_mapping(port->pirq.domain, PORT_SRC_PTP_INT);
-	if (ptpirq->irq_num < 0) {
-		ret = ptpirq->irq_num;
+	if (!ptpirq->irq_num) {
+		ret = -EINVAL;
 		goto out;
 	}
 

-- 
2.51.1