u-boot: Update ref (add DT overlay support)

  mediatek: mt7986: Enable FDT overlay support

package/boot/uboot-mediatek/Makefile

@@ -4,7 +4,7 @@ include $(INCLUDE_DIR)/kernel.mk
 PKG_VERSION:=2022.04
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL:=https://dev.iopsys.eu/fork/u-boot.git
-PKG_SOURCE_VERSION:=6ed50bce051d79baf770f40fdfefdab201baf92a
+PKG_SOURCE_VERSION:=cd6131e69d836ed8e9818e821a18bff11ff621dd
 PKG_VERSION:=2022-04-$(PKG_SOURCE_VERSION)
 PKG_BUILD_DEPENDS:=arm-trusted-firmware-tools/host
 PKG_MIRROR_HASH:=skip