arm64: dts: imx8mm-nitrogen-r2: rework UART 2

Remove useless clocks in UART 2
Signed-off-by: Adrien Grassein <adrien.grassein@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mm-nitrogen-r2.dts

@@ -210,8 +210,6 @@ &uart1 {
 &uart2 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_uart2>;
-	assigned-clocks = <&clk IMX8MM_CLK_UART2>;
-	assigned-clock-parents = <&clk IMX8MM_CLK_24M>;
 	status = "okay";
 };