payloads/U-boot: Fix U-Boot cloning error

Renaming origin/master to just master fix error during cloning repo.
Error: Remote branch origin/master not found in upstream origin

Change-Id: Ib5d4bb0277076842f8a8400eb61da9ad23465b66
Signed-off-by: eliassouza <eliascontato@protonmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/72464
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
diff --git a/payloads/external/U-Boot/Makefile b/payloads/external/U-Boot/Makefile
index 07b6f48..c29fe2b 100644
--- a/payloads/external/U-Boot/Makefile
+++ b/payloads/external/U-Boot/Makefile
@@ -1,6 +1,6 @@
 ## SPDX-License-Identifier: GPL-2.0-only
 
-TAG-$(CONFIG_UBOOT_MASTER)=origin/master
+TAG-$(CONFIG_UBOOT_MASTER)=master
 TAG-$(CONFIG_UBOOT_STABLE)=$(STABLE_COMMIT_ID)
 
 project_name=U-Boot