Currently, the function follows the usual pattern used in our code:

  int ret = -1;
  ...
  ret = 0;
 cleanup:
  return ret;

However, the function always call exit() on error, so the cleanup
label is never jumped onto. Therefore, it doesn't make any sense to
have the parse_argv function return an integer value, if it
effectively can return only value of zero.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>