clutter-gstreamer: fix a typo

corrent ->
correct
     ^

Reported by Toyo Abe. Thanks!!!

They are derived from the original Clutter-GStreamer. We should report
them to upstream but they are already removed:
  https://git.gnome.org/browse/clutter-gst/commit/examples/video-sink-navigation.c?id=97b1e5ad8c4cabe68553bf4138b1ae5d12535ec3

So we need to report them. (But we need to update the sample.)