dts: imx8mq-librem5: Describe MIC_2V4 regulator

No functional change, but it describes the hardware better.

arch/arm64/boot/dts/freescale/imx8mq-librem5.dtsi

@@ -181,6 +181,14 @@ reg_aud_1v8: regulator-audio-1v8 {
 		vin-supply = <&reg_audio_pwr_en>;
 	};
 
+	reg_mic_2v4: regulator-mic-2v4 {
+		compatible = "regulator-fixed";
+		regulator-name = "MIC_2V4";
+		regulator-min-microvolt = <2400000>;
+		regulator-max-microvolt = <2400000>;
+		vin-supply = <&reg_audio_pwr_en>;
+	};
+
 	/*
 	 * the pinctrl for reg_csi_1v8 and reg_vcam_1v8 is added to the PMIC
 	 * since we can't have those 2 times on the 2 different regulators.
@@ -1314,7 +1322,7 @@ codec: audio-codec@1a {
 		DBVDD-supply = <&reg_aud_1v8>;
 		AVDD-supply = <&reg_aud_1v8>;
 		CPVDD-supply = <&reg_aud_1v8>;
-		MICVDD-supply = <&reg_aud_1v8>;
+		MICVDD-supply = <&reg_mic_2v4>;
 		PLLVDD-supply = <&reg_aud_1v8>;
 		SPKVDD1-supply = <&reg_vsys_3v4>;
 		SPKVDD2-supply = <&reg_vsys_3v4>;