staging: media: ipu3: Stop streaming in inverse order of starting

imgu_vb2_stop_streaming() did not order shutdown items in the inverse
order and count of what imgu_vb2_start_streaming() does. Consequently,
v6.7's new WARN_ON in call_s_stream() started screaming because it was
called multiple times on the entire pipe, yet it should only be called
when the pipe is interrupted by any first node being taken offline.

This reorders streamoff to be the inverse of streamon, and uses
analogous conditions to decide when and how often to call additional
teardown functions.

v4l2_subdev_call(s_stream, 0) remains outside the streaming_lock,
analogously to imgu_vb2_start_streaming().

Signed-off-by: Max Staudt <mstaudt@chromium.org>
Reviewed-by: Bingbu Cao <bingbu.cao@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>