buildman: Clean up odd characters on the terminal

At present buildman leaves behind a few characters during its progress
updates, which looks odd. Fix it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/builder.py b/tools/buildman/builder.py
index 6905ed9..236e061 100644
--- a/tools/buildman/builder.py
+++ b/tools/buildman/builder.py
@@ -443,7 +443,7 @@
 
         name += target
         Print(line + name, newline=False)
-        length = 14 + len(name)
+        length = 16 + len(name)
         self.ClearLine(length)
 
     def _GetOutputDir(self, commit_upto):