payloads/filo: Update branch name from master to main

It seems like the default branch for FILO was renamed from 'master' to
'main'.

TEST: FILO builds correctly when selecting 'HEAD' for the FILO version
option.

Change-Id: I6c355d757987551e850f9d24f6bfb14167cb8046
Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76101
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

payloads/external/FILO/Kconfig

@@ -9,7 +9,7 @@ config FILO_STABLE
 	help
 	  Tested FILO version
 
-config FILO_MASTER
+config FILO_HEAD
 	bool "HEAD"
 	help
 	  Newest FILO version

payloads/external/FILO/Makefile

@@ -1,5 +1,5 @@
-TAG-$(CONFIG_FILO_MASTER)=origin/master
-NAME-$(CONFIG_FILO_MASTER)=MASTER
+TAG-$(CONFIG_FILO_HEAD)=origin/main
+NAME-$(CONFIG_FILO_HEAD)=MAIN
 TAG-$(CONFIG_FILO_STABLE)=c2fa1ea6125c63e84cdf7779c37d76da8c5bc412
 NAME-$(CONFIG_FILO_STABLE)=STABLE
 
@@ -20,7 +20,7 @@ checkout:
 	test -d filo || \
 		git clone $(project_git_repo) $(project_dir)
 	cd filo && \
-		git checkout master && \
+		git checkout main && \
 		git remote update && \
 		test -n $(TAG-y) && \
 			git branch -f $(NAME-y) $(TAG-y) && \