doc: media: v4l/func-open.rst: ENXIO should be ENODEV

The error that V4L2 returns when an attempt is made to open an
unregisted device node is ENODEV, no ENXIO. Update the documentation.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

Documentation/userspace-api/media/v4l/func-open.rst

@@ -65,8 +65,8 @@ EBUSY
     The driver does not support multiple opens and the device is already
     in use.
 
-ENXIO
-    No device corresponding to this device special file exists.
+ENODEV
+    Device not found or was removed.
 
 ENOMEM
     Not enough kernel memory was available to complete the request.