media: Documentation: Additional streams generally don't harm capture

Having extra streams on the source end of the link that cannot be captured
by the sink sub-device generally are not an issue, at least not on CSI-2
bus. Still document that there may be hardware-specific limitations. For
example on parallel bus this might not work on all cases.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

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

@@ -529,9 +529,9 @@ the its sink pad and allows to route them individually to one of its source
 pads.
 
 Subdevice drivers that support multiplexed streams are compatible with
-non-multiplexed subdev drivers, but, of course, require a routing configuration
-where the link between those two types of drivers contains only a single
-stream.
+non-multiplexed subdev drivers. However, if the driver at the sink end of a link
+does not support streams, then only stream 0 of source end may be captured.
+There may be additional limitations specific to the sink device.
 
 Understanding streams
 ^^^^^^^^^^^^^^^^^^^^^