The pointed MouseTransformInfo structure is accessed read-only.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20221220142520.24094-2-philmd@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>