video: fix typo in video_sync_all documentation

%s/there/their/

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/video.h b/include/video.h
index 2699151..16f7a83 100644
--- a/include/video.h
+++ b/include/video.h
@@ -260,7 +260,7 @@
 int video_sync(struct udevice *vid, bool force);
 
 /**
- * video_sync_all() - Sync all devices' frame buffers with there hardware
+ * video_sync_all() - Sync all devices' frame buffers with their hardware
  *
  * This calls video_sync() on all active video devices.
  */