ramips: mt7621-dts: fix phy-mode of external phy on GB-PC2

The phy-mode property must be defined on the MAC instead of the PHY. Define
phy-mode under gmac1 which the external phy is connected to.

Tested-by: Petr Louda <petr.louda@outlook.cz>
Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>

target/linux/ramips/dts/mt7621_gnubee_gb-pc2.dts

@@ -118,6 +118,7 @@
 &gmac1 {
 	status = "okay";
 	label = "ethyellow";
+	phy-mode = "rgmii-rxid";
 	phy-handle = <&ethphy5>;
 
 	nvmem-cells = <&macaddr_factory_e000>;
@@ -127,7 +128,6 @@
 &mdio {
 	ethphy5: ethernet-phy@5 {
 		reg = <5>;
-		phy-mode = "rgmii-rxid";
 	};
 };