arm64: dts: fix mdio pinctrl based on binding

Author: frank-w

arch/arm64/boot/dts/mediatek/mt7988a.dtsi

@@ -323,7 +323,7 @@
 				};
 
 				conf {
-					groups = "mdc_mdio0";
+					pins = "SMI_0_MDC", "SMI_0_MDIO";
 					drive-strength = <MTK_DRIVE_8mA>;
 				};
 			};