arm: dts: mediatek: convert gmac link mode to 2500base-x for r3

Ethernet on Bananapi-r3 is broken after

commit bd70f3cea353 ("net: mediatek: add support for SGMII 1Gbps auto-negotiation mode")

because changes from this commit were not applied to bpi-r3 devicetree too:

commit aef54ea16cac ("arm: dts: medaitek: convert gmac link mode to 2500base-x")

Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
diff --git a/arch/arm/dts/mt7986a-bpi-r3-sd.dts b/arch/arm/dts/mt7986a-bpi-r3-sd.dts
index 1525630..c156a81 100644
--- a/arch/arm/dts/mt7986a-bpi-r3-sd.dts
+++ b/arch/arm/dts/mt7986a-bpi-r3-sd.dts
@@ -76,12 +76,12 @@
 &eth {
 	status = "okay";
 	mediatek,gmac-id = <0>;
-	phy-mode = "sgmii";
+	phy-mode = "2500base-x";
 	mediatek,switch = "mt7531";
 	reset-gpios = <&gpio 5 GPIO_ACTIVE_HIGH>;
 
 	fixed-link {
-		speed = <1000>;
+		speed = <2500>;
 		full-duplex;
 	};
 };