media: videobuf2: set q->streaming later

Commit a10b2153 ("media: vb2: add (un)prepare_streaming queue ops") moved
up the q->streaming = 1 assignment to before the call to vb2_start_streaming().

This does make sense since q->streaming indicates that VIDIOC_STREAMON is called,
and the call to start_streaming happens either at that time or later if
q->min_buffers_needed > 0. So q->streaming should be 1 before start_streaming
is called.

However, it turned out that some drivers use vb2_is_streaming() in buf_queue,
and if q->min_buffers_needed == 0, then that will now return true instead of
false.

So for the time being revert to the original behavior.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Fixes: a10b2153 ("media: vb2: add (un)prepare_streaming queue ops")
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>