fix patman --limit-cc option

fix patman --limit-cc option

patman's --limit-cc option parses its argument to an integer and uses
that to trim the list of CC recipients to a particular maximum. but that
only works if the cc variable is a list, which it is not.

Signed-off-by: Bernhard Kirchen <bernhard.kirchen@mbconnectline.com>
Reviewed-by: Simon Glass <sjg@chromium.org>