arm: dts: imx8mm: drop assigned clocks for clk node

Drop assigned clocks for clk node, this will break boot on i.MX8MM EVK
board.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/dts/imx8mm-evk-u-boot.dtsi b/arch/arm/dts/imx8mm-evk-u-boot.dtsi
index 16093f2..f62a7cf 100644
--- a/arch/arm/dts/imx8mm-evk-u-boot.dtsi
+++ b/arch/arm/dts/imx8mm-evk-u-boot.dtsi
@@ -11,6 +11,9 @@
 &clk {
 	u-boot,dm-spl;
 	u-boot,dm-pre-reloc;
+	/delete-property/ assigned-clocks;
+	/delete-property/ assigned-clock-parents;
+	/delete-property/ assigned-clock-rates;
 };
 
 &osc_24m {