ar71xx: ag71xx: Prevent kernel oops for board def

The driver is written in such a way that with a board defintion that
connects a fixed phy, mdio, and switch in a certain way, a kernel oops could
result because of lack of previously probed mdio bus.

This commit allows for easier debugging in this case by casting the
correct blame with serial console messages.

Signed-off-by: Daniel F. Dickinson <cshored@thecshore.com>

target/linux/ar71xx/files/drivers/net/ethernet/atheros/ag71xx/ag71xx_phy.c

@@ -76,10 +76,24 @@ void ag71xx_phy_stop(struct ag71xx *ag)
 
 static int ag71xx_phy_connect_fixed(struct ag71xx *ag)
 {
-	struct device *dev = &ag->pdev->dev;
+	struct platform_device *pdev = ag->pdev;
+	struct device *dev = NULL;
 	struct ag71xx_platform_data *pdata = ag71xx_get_pdata(ag);
 	int ret = 0;
 
+	if (!pdev)
+		return -ENODEV;
+
+	dev = &pdev->dev;
+
+	if (!dev)
+		return -ENODEV;
+
+	if (!ag->phy_dev) {
+		pr_err("Missing PHY for %s", dev_name(dev));
+		return -ENODEV;
+	}
+
 	/* use fixed settings */
 	switch (pdata->speed) {
 	case SPEED_10: