branch: fix a leak in setup_tracking

branch: fix a leak in setup_tracking

In bdaf1dfae7 (branch: new autosetupmerge option "simple" for matching
branches, 2022-04-29) a new exit for setup_tracking() missed the
clean-up, producing a leak.

   $ git config branch.autoSetupMerge simple
   $ git remote add local .
   $ git update-ref refs/remotes/local/foo HEAD
   $ git branch bar local/foo

   Direct leak of 384 byte(s) in 1 object(s) allocated from:
       ... in xrealloc wrapper.c
       ... in string_list_append_nodup string-list.c
       ... in find_tracked_branch branch.c
       ... in for_each_remote remote.c
       ... in setup_tracking branch.c
       ... in create_branch branch.c
       ... in cmd_branch builtinbranch.c
       ... in run_builtin git.c

   Indirect leak of 24 byte(s) in 1 object(s) allocated from:
       ... in xrealloc wrapper.c
       ... in strbuf_grow strbuf.c
       ... in strbuf_add strbuf.c
       ... in match_name_with_pattern remote.c
       ... in query_refspecs remote.c
       ... in remote_find_tracking remote.c
       ... in find_tracked_branch branch.c
       ... in for_each_remote remote.c
       ... in setup_tracking branch.c
       ... in create_branch branch.c
       ... in cmd_branch builtinbranch.c
       ... in run_builtin git.c

The return introduced in bdaf1dfae7 was to avoid setting up the
tracking, but even in that case it is still necessary to do the
clean-up.  Let's do it.

Signed-off-by: Rubén Justo <rjusto@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>