dt-bindings: ata: highbank: Minor whitespace cleanup in example

The DTS code coding style expects exactly one space around '='
character.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>