drm/ioc32: replace __attribute__((packed)) with __packed

__packed is preferred over __attribute__((packed)).

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Simon Ser <contact@emersion.fr>
Link: https://patchwork.freedesktop.org/patch/msgid/20231212132557.3777281-2-jani.nikula@intel.com