[928][DTS] set correct phy-mode for RGMII Gigabit Ethernet

arch/arm/boot/dts/seco/seco-imx6qdl-928.dtsi

@@ -464,7 +464,7 @@ &usdhc4 {
 &fec {
 	pinctrl-names        = "default";
 	pinctrl-0            = <&pinctrl_enet>;
-	phy-mode             = "rgmii";
+	phy-mode             = "rgmii-id";
 	phy-reset-gpios      = <&gpio3 23 GPIO_ACTIVE_LOW>;
 	phy-handle           = <&ethphy0>;
 	phy-reset-duration   = <10>;