drm: rcar-du: kms: Expand comment in vsps parsing routine

Expand comment in the 'vsps' parsing routine to specify the LIF
channel index defaults to 0 in case the second cell of the property
is not specified to remain compatible with older DT bindings.
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

drivers/gpu/drm/rcar-du/rcar_du_kms.c

@@ -585,7 +585,11 @@ static int rcar_du_vsps_init(struct rcar_du_device *rcdu)
 
 		vsps[j].crtcs_mask |= BIT(i);
 
-		/* Store the VSP pointer and pipe index in the CRTC. */
+		/*
+		 * Store the VSP pointer and pipe index in the CRTC. If the
+		 * second cell of the 'vsps' specifier isn't present, default
+		 * to 0 to remain compatible with older DT bindings.
+		 */
 		rcdu->crtcs[i].vsp = &rcdu->vsps[j];
 		rcdu->crtcs[i].vsp_pipe = cells >= 1 ? args.args[0] : 0;
 	}