hw/sd/sdcard: Explicit dummy byte value

On error the DAT lines are left unmodified to their
previous states. QEMU returns 0x00 for convenience.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20240730092138.32443-2-philmd@linaro.org>
1 file changed