The AST2600 EVB A1 board should have dedicated compatible.

Fixes: a7295518 ("ARM: dts: aspeed: ast2600evb: Add dts file for A1 and A0")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220529104928.79636-6-krzysztof.kozlowski@linaro.org