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.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/surface_aggregator/device.h

@@ -229,10 +229,7 @@ static inline bool is_ssam_device(struct device *d)
  * Return: Returns a pointer to the &struct ssam_device wrapping the given
  * device @d.
  */
-static inline struct ssam_device *to_ssam_device(struct device *d)
-{
-	return container_of(d, struct ssam_device, dev);
-}
+#define to_ssam_device(d)	container_of_const(d, struct ssam_device, dev)
 
 /**
  * to_ssam_device_driver() - Casts the given device driver to a SSAM client