clearfog: Use a released U-Boot version

Change-Id: If2083c8ef5e7ab944ac47a210c30990cdc953b5c
diff --git a/configs/czechlight_clearfog_defconfig b/configs/czechlight_clearfog_defconfig
index 482f07d..f2e38ab 100644
--- a/configs/czechlight_clearfog_defconfig
+++ b/configs/czechlight_clearfog_defconfig
@@ -57,7 +57,7 @@
 BR2_TARGET_UBOOT_BUILD_SYSTEM_KCONFIG=y
 BR2_TARGET_UBOOT_CUSTOM_GIT=y
 BR2_TARGET_UBOOT_CUSTOM_REPO_URL="https://gerrit.cesnet.cz/github/trini/u-boot"
-BR2_TARGET_UBOOT_CUSTOM_REPO_VERSION="v2018.09-rc3"
+BR2_TARGET_UBOOT_CUSTOM_REPO_VERSION="v2018.09"
 BR2_TARGET_UBOOT_PATCH="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/clearfog/patches/u-boot/boot.patch"
 BR2_TARGET_UBOOT_BOARD_DEFCONFIG="clearfog"
 BR2_TARGET_UBOOT_CONFIG_FRAGMENT_FILES="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/clearfog/uboot.fragment"