media: vsp1: Remove unbalanced .s_stream(0) calls

The VSP1 driver uses the subdev .s_stream() operation to stop WPF
instances, without a corresponding call to start them. The V4L2 subdev
core started warning about unbalanced .s_stream() calls in commit
009905ec ("media: v4l2-subdev: Document and enforce .s_stream()
requirements"), causing a regression with this driver.

Fix the problem by replacing the .s_stream() operation with an explicit
function call for WPF instances. This allows sharing an additional data
structure between RPF and WPF instances.

Fixes: 009905ec ("media: v4l2-subdev: Document and enforce .s_stream() requirements")
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Closes: https://lore.kernel.org/linux-media/2221395-6a9b-9527-d697-e76aebc6af@linux-m68k.org/


Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>