[Aarch64] Fix warning in _sbrk

[Christophe Lyon]

ping?
On Mon, 1 Oct 2018 at 23:34, Christophe Lyon <christophe.lyon@linaro.org> wrote:
>
> Hi,
>
> While building newlib for Aarch64, I noticed a warning in _sbrk. This
> small patch fixes it the same way it is done in the Arm version.
>
> OK?
>
> Christophe