[media] em28xx: Fix return value for s_ctrl

On some cases, driver returns 1. This should be OK, but qv4l2 is too
strict about return values.
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/em28xx/em28xx-video.c

@@ -1452,7 +1452,7 @@ static int vidioc_s_ctrl(struct file *file, void *priv,
 			rc = em28xx_audio_analog_set(dev);
 		}
 	}
-	return rc;
+	return (rc < 0) ? rc : 0;
 }
 
 static int vidioc_g_tuner(struct file *file, void *priv,