tools/dep-tree: show usage with --help

Signed-off-by: Robert Langhammer <rlanghammer@web.de>

tools/dep-tree

@@ -10,6 +10,8 @@ usage() {
 	EOF
 }
 
+[ $1 = "-h" -o $1 = "--help" ] && usage && exit
+
 builddir=./build
 variant=$(cat selected_variant)
 [ $# = 0 ] || variant="$@"
@@ -43,7 +45,6 @@ done
 echo "digraph G {"
 sort "$tmpfile" | uniq | grep -v libc | grep -v libssp | grep -v libpthread | grep -v librt
 echo "}"
-[ -s $tmpfile ] || usage
 rm "$tmpfile"