fix linespec bug noticed by the checker

fix linespec bug noticed by the checker

This fixes a linespec bug noticed by the cleanup checker.

find_linespec_symbols did this:

  cleanup = demangle_for_lookup (name, state->language->la_language,
				 &lookup_name);
[...]
      cleanup = make_cleanup (xfree, canon);

But this is wrong, as it makes a subsequent call to do_cleanups not
clean up all the local state.

	* linespec.c (find_linespec_symbols): Don't reassign to 'cleanup'.