ARM: dts: imx6ul: fix clock frequency property name of I2C buses

A few boards set clock frequency of their I2C buses with
"clock_frequency" property. The right property is "clock-frequency".
Signed-off-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6ul-14x14-evk.dtsi

@@ -112,7 +112,7 @@ &clks {
 };
 
 &i2c2 {
-	clock_frequency = <100000>;
+	clock-frequency = <100000>;
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_i2c2>;
 	status = "okay";

arch/arm/boot/dts/imx6ul-geam.dts

@@ -156,7 +156,7 @@ sgtl5000: codec@a {
 };
 
 &i2c2 {
-	clock_frequency = <100000>;
+	clock-frequency = <100000>;
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_i2c2>;
 	status = "okay";

arch/arm/boot/dts/imx6ul-isiot.dtsi

@@ -148,7 +148,7 @@ stmpe: touchscreen {
 };
 
 &i2c2 {
-	clock_frequency = <100000>;
+	clock-frequency = <100000>;
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_i2c2>;
 	status = "okay";

arch/arm/boot/dts/imx6ul-pico-hobbit.dts

@@ -43,7 +43,7 @@ sys_mclk: clock-sys-mclk {
 };
 
 &i2c2 {
-	clock_frequency = <100000>;
+	clock-frequency = <100000>;
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_i2c2>;
 	status = "okay";

arch/arm/boot/dts/imx6ul-pico-pi.dts

@@ -43,7 +43,7 @@ sys_mclk: clock-sys-mclk {
 };
 
 &i2c2 {
-	clock_frequency = <100000>;
+	clock-frequency = <100000>;
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_i2c2>;
 	status = "okay";
@@ -58,7 +58,7 @@ sgtl5000: codec@a {
 };
 
 &i2c3 {
-	clock_frequency = <100000>;
+	clock-frequency = <100000>;
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_i2c3>;
 	status = "okay";