net: lan966x: check for ptp to be enabled in lan966x_ptp_deinit()

If ptp was not enabled due to missing IRQ for instance,
lan966x_ptp_deinit() will dereference NULL pointers.

Fixes: d0964594 ("net: lan966x: Add support for ptp clocks")
Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Reviewed-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/microchip/lan966x/lan966x_ptp.c

@@ -1073,6 +1073,9 @@ void lan966x_ptp_deinit(struct lan966x *lan966x)
 	struct lan966x_port *port;
 	int i;
 
+	if (!lan966x->ptp)
+		return;
+
 	for (i = 0; i < lan966x->num_phys_ports; i++) {
 		port = lan966x->ports[i];
 		if (!port)