drivers: ksz8081: Fix fault on boot in handler thread

Issue was that the gpio interrupt was happening before the work item was
initialized, and then trying to schedule it, resulting null pointer
dereference and fault occurring.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>

Author: decsny

drivers/ethernet/phy/phy_microchip_ksz8081.c

@@ -61,6 +61,7 @@ struct mc_ksz8081_config {
 #define KSZ8081_DO_AUTONEG_FLAG BIT(0)
 #define KSZ8081_SILENCE_DEBUG_LOGS BIT(1)
 #define KSZ8081_LINK_STATE_VALID BIT(2)
+#define KSZ8081_INITIALIZED BIT(3)
 
 #define USING_INTERRUPT_GPIO							\
 		UTIL_OR(DT_ALL_INST_HAS_PROP_STATUS_OKAY(int_gpios),		\
@@ -183,7 +184,11 @@ static void phy_mc_ksz8081_interrupt_handler(const struct device *port, struct g
 					     gpio_port_pins_t pins)
 {
 	struct mc_ksz8081_data *data = CONTAINER_OF(cb, struct mc_ksz8081_data, gpio_callback);
-	int ret = k_work_reschedule(&data->phy_monitor_work, K_NO_WAIT);
+	int ret = -ESRCH;
+
+	if (data->flags & KSZ8081_INITIALIZED) {
+		ret = k_work_reschedule(&data->phy_monitor_work, K_NO_WAIT);
+	}
 
 	if (ret < 0) {
 		LOG_ERR("Failed to schedule monitor_work from ISR");
@@ -689,17 +694,19 @@ static int phy_mc_ksz8081_init(const struct device *dev)
 		return ret;
 	}
 
-	ret = ksz8081_init_int_gpios(dev);
-	if (ret < 0) {
-		return ret;
-	}
-
 	k_work_init_delayable(&data->phy_monitor_work,
 				phy_mc_ksz8081_monitor_work_handler);
 
 	/* Advertise default speeds */
 	phy_mc_ksz8081_cfg_link(dev, config->default_speeds, 0);
 
+	ret = ksz8081_init_int_gpios(dev);
+	if (ret < 0) {
+		return ret;
+	}
+
+	data->flags |= KSZ8081_INITIALIZED;
+
 	return 0;
 }