media: Documentation: v4l: Fix ACTIVE route flag

The documentation in one occasion mentions the
VIDIOC_SUBDEV_STREAM_FL_ACTIVE flag. This was meant to be
V4L2_SUBDEV_STREAM_FL_ACTIVE as it's a flag, not an IOCTL. Fix it.

Fixes: cd2c75454d74 ("media: Documentation: Document S_ROUTING behaviour")
Reported-by: Samuel Wein PhD <[e-mail]>
Signed-off-by: Sakari Ailus <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>

Documentation/userspace-api/media/v4l/dev-subdev.rst

···
 Devices generating the streams may allow enabling and disabling some of the
 routes or have a fixed routing configuration. If the routes can be disabled, not
 declaring the routes (or declaring them without
-``VIDIOC_SUBDEV_STREAM_FL_ACTIVE`` flag set) in ``VIDIOC_SUBDEV_S_ROUTING`` will
+``V4L2_SUBDEV_STREAM_FL_ACTIVE`` flag set) in ``VIDIOC_SUBDEV_S_ROUTING`` will
 disable the routes. ``VIDIOC_SUBDEV_S_ROUTING`` will still return such routes
 back to the user in the routes array, with the ``V4L2_SUBDEV_STREAM_FL_ACTIVE``
 flag unset.