media: vsp1: Use vb2_queue_is_busy()

Use the new vb2_queue_is_busy() helper to replace the open-coded
version.

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