ARM: dts: stm32f429: Fix Ethernet node on Eval Board

"phy-handle" entry is mandatory when mdio subnode is used in
Ethernet node.
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32429i-eval.dts

@@ -121,7 +121,7 @@ &mac {
 	pinctrl-0	= <&ethernet_mii>;
 	pinctrl-names	= "default";
 	phy-mode	= "mii";
-
+	phy-handle	= <&phy1>;
 	mdio0 {
 		#address-cells = <1>;
 		#size-cells = <0>;