The AST2500 EVB board should have dedicated compatible.

Fixes: 02440622 ("arm/dst: Add Aspeed ast2500 device tree")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220529104928.79636-4-krzysztof.kozlowski@linaro.org