ARM: dts: ast2500-evb: fix board compatible

[ Upstream commit 30b276fca5c0644f3cb17bceb1bd6a626c670184 ]

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


Signed-off-by: Sasha Levin <sashal@kernel.org>