Revert "ar71xx: ag71xx: Prevent kernel oops for board def"

This reverts commit 7a3e133751.

This change reportedly breaks connectivity on some ar71xx devices, so
revert it for now.

Ref: https://github.com/openwrt/openwrt/pull/1217#issuecomment-409708087
Reported-by: Hannu Nyman <hannu.nyman@iki.fi>
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

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

@@ -76,24 +76,10 @@ void ag71xx_phy_stop(struct ag71xx *ag)
 
 static int ag71xx_phy_connect_fixed(struct ag71xx *ag)
 {
-	struct platform_device *pdev = ag->pdev;
-	struct device *dev = NULL;
+	struct device *dev = &ag->pdev->dev;
 	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: