arm64: dts: imx8mm-beacon-som: Align regulator names with schema

Device tree schema expects regulator names to be lowercase.  This fixes
dtbs_check warnings like:

    pmic@4b: regulators:LDO1:regulator-name:0: 'LDO1' does not match '^ldo[1-6]$'
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mm-beacon-som.dtsi

@@ -79,7 +79,7 @@ pmic@4b {
 
 		regulators {
 			buck1_reg: BUCK1 {
-				regulator-name = "BUCK1";
+				regulator-name = "buck1";
 				regulator-min-microvolt = <700000>;
 				regulator-max-microvolt = <1300000>;
 				regulator-boot-on;
@@ -88,7 +88,7 @@ buck1_reg: BUCK1 {
 			};
 
 			buck2_reg: BUCK2 {
-				regulator-name = "BUCK2";
+				regulator-name = "buck2";
 				regulator-min-microvolt = <700000>;
 				regulator-max-microvolt = <1300000>;
 				regulator-boot-on;
@@ -100,7 +100,7 @@ buck2_reg: BUCK2 {
 
 			buck3_reg: BUCK3 {
 				// BUCK5 in datasheet
-				regulator-name = "BUCK3";
+				regulator-name = "buck3";
 				regulator-min-microvolt = <700000>;
 				regulator-max-microvolt = <1350000>;
 				regulator-boot-on;
@@ -109,7 +109,7 @@ buck3_reg: BUCK3 {
 
 			buck4_reg: BUCK4 {
 				// BUCK6 in datasheet
-				regulator-name = "BUCK4";
+				regulator-name = "buck4";
 				regulator-min-microvolt = <3000000>;
 				regulator-max-microvolt = <3300000>;
 				regulator-boot-on;
@@ -118,7 +118,7 @@ buck4_reg: BUCK4 {
 
 			buck5_reg: BUCK5 {
 				// BUCK7 in datasheet
-				regulator-name = "BUCK5";
+				regulator-name = "buck5";
 				regulator-min-microvolt = <1605000>;
 				regulator-max-microvolt = <1995000>;
 				regulator-boot-on;
@@ -127,7 +127,7 @@ buck5_reg: BUCK5 {
 
 			buck6_reg: BUCK6 {
 				// BUCK8 in datasheet
-				regulator-name = "BUCK6";
+				regulator-name = "buck6";
 				regulator-min-microvolt = <800000>;
 				regulator-max-microvolt = <1400000>;
 				regulator-boot-on;
@@ -135,7 +135,7 @@ buck6_reg: BUCK6 {
 			};
 
 			ldo1_reg: LDO1 {
-				regulator-name = "LDO1";
+				regulator-name = "ldo1";
 				regulator-min-microvolt = <1600000>;
 				regulator-max-microvolt = <3300000>;
 				regulator-boot-on;
@@ -143,7 +143,7 @@ ldo1_reg: LDO1 {
 			};
 
 			ldo2_reg: LDO2 {
-				regulator-name = "LDO2";
+				regulator-name = "ldo2";
 				regulator-min-microvolt = <800000>;
 				regulator-max-microvolt = <900000>;
 				regulator-boot-on;
@@ -151,7 +151,7 @@ ldo2_reg: LDO2 {
 			};
 
 			ldo3_reg: LDO3 {
-				regulator-name = "LDO3";
+				regulator-name = "ldo3";
 				regulator-min-microvolt = <1800000>;
 				regulator-max-microvolt = <3300000>;
 				regulator-boot-on;
@@ -159,7 +159,7 @@ ldo3_reg: LDO3 {
 			};
 
 			ldo4_reg: LDO4 {
-				regulator-name = "LDO4";
+				regulator-name = "ldo4";
 				regulator-min-microvolt = <900000>;
 				regulator-max-microvolt = <1800000>;
 				regulator-boot-on;
@@ -167,7 +167,7 @@ ldo4_reg: LDO4 {
 			};
 
 			ldo6_reg: LDO6 {
-				regulator-name = "LDO6";
+				regulator-name = "ldo6";
 				regulator-min-microvolt = <900000>;
 				regulator-max-microvolt = <1800000>;
 				regulator-boot-on;