media: vsp1: Document vsp1_dl_body refcnt

In commit 2d9445db0e ("media: vsp1: Use reference counting for
bodies"), a new field was introduced to the vsp1_dl_body structure to
account for usage tracking of the body.

Document the newly added field in the kerneldoc.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/platform/vsp1/vsp1_dl.c

@@ -43,6 +43,7 @@ struct vsp1_dl_entry {
  * struct vsp1_dl_body - Display list body
  * @list: entry in the display list list of bodies
  * @free: entry in the pool free body list
+ * @refcnt: reference tracking for the body
  * @pool: pool to which this body belongs
  * @vsp1: the VSP1 device
  * @entries: array of entries