u-boot-libre: help: fix version line

While technically the version is optional, the line being printed
only describes runinng this script with a given version.

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>

resources/scripts/build/release/u-boot-libre

@@ -47,7 +47,7 @@ usage()
 	printf "\t%s                  # %s\n" \
 	       "${progname}" \
 	       "Release deblobbed u-boot tarballs for all supported versions"
-	printf "\t%s [version]        # %s\n" \
+	printf "\t%s <version>        # %s\n" \
 	       "${progname}" \
 	       "Release deblobbed u-boot tarballs for the given version"
 	printf "\t%s --list-versions  # %s\n" \