[gold][aarch64]: Use "gold_info" instead of "gold_warning" for erratum fix

[Cary Coutant]

> gold/ChangeLog:
>
>         * aarch64.cc (Target_aarch64::scan_erratum_843419_span): Use
> 'gold_info'.
>         (Target_aarch64::scan_erratum_835769_span): Use 'gold_info'.

This is OK. Thanks!

-cary