hw/core/cpu: Use size_t for memory_rw_debug len argument

hw/core/cpu: Use size_t for memory_rw_debug len argument

Match the prototype of cpu_memory_rw_debug().

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20250325224403.4011975-4-richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>