hw/gpio/aspeed: Fix definition of AspeedGPIOClass

hw/gpio/aspeed: Fix definition of AspeedGPIOClass

AspeedGPIOClass's parent is SysBusDeviceClass rather than SysBusDevice.
This isn't catastrophic only because sizeof(SysBusDevice) >
sizeof(SysBusDeviceClass).

Fixes: 4b7f956862dc ("hw/gpio: Add basic Aspeed GPIO model for AST2400 and AST2500")
Closes: https://lists.gnu.org/archive/html/qemu-devel/2025-06/msg00586.html
Suggested-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Message-ID: <20250606092406.229833-4-zhenzhong.duan@intel.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>