[media] v4l2-ioctl: clarify querystd comment

Improve the querystd comment.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/v4l2-core/v4l2-ioctl.c

@@ -1385,10 +1385,10 @@ static int v4l_querystd(const struct v4l2_ioctl_ops *ops,
 	v4l2_std_id *p = arg;
 
 	/*
-	 * If nothing detected, it should return all supported
-	 * standard.
-	 * Drivers just need to mask the std argument, in order
-	 * to remove the standards that don't apply from the mask.
+	 * If no signal is detected, then the driver should return
+	 * V4L2_STD_UNKNOWN. Otherwise it should return tvnorms with
+	 * any standards that do not apply removed.
+	 *
 	 * This means that tuners, audio and video decoders can join
 	 * their efforts to improve the standards detection.
 	 */