platform/surface: aggregator: move to_ssam_device() to use container_of_const()

platform/surface: aggregator: move to_ssam_device() to use container_of_const()

The driver core is changing to pass some pointers as const, so move
to_ssam_device() to use container_of_const() to handle this change.
to_ssam_device() now properly keeps the const-ness of the pointer passed
into it, while as before it could be lost.

Reviewed-by: Maximilian Luz <luzmaximilian@gmail.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20230111113018.459199-4-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>