dts: xea: Remove clocks property from debug UART on XEA

The imx287 SoC doesn't support common clock framework (CCF), so the
'clocks' property is removed to avoid early (i.e. in SPL) errors when
SPL_OF_PLATDATA is used.

Signed-off-by: Lukasz Majewski <lukma@denx.de>

arch/arm/dts/imx28-xea-u-boot.dtsi

@@ -35,6 +35,7 @@
 };
 
 &duart {
+	/delete-property/ clocks;
 	bootph-pre-ram;
 	type = <1>; /* TYPE_PL011 */
 };