patman: Start with a clean series when needed

patman: Start with a clean series when needed

For reasons that are not well-understood, GetMetaDataForList() can end up
adding to an existing series even when it appears that it should be
starting a new one.

Change from using a default constructor parameter to an explicit one, to
work around this problem.

Signed-off-by: Simon Glass <sjg@chromium.org>