Revert "Typo in pl_Release();"

This reverts commit 9bddd7d3.

By its current design, pl_Release() takes the same argument as
pl_Yield(). This had _already_ been discussed earlier (vlc-devel is not
a write-only mailing list).

src/video_output/vout_intf.c

@@ -1199,7 +1199,7 @@ static int OnTopCallback( vlc_object_t *p_this, char const *psz_cmd,
     var_Create( p_playlist, "video-on-top", VLC_VAR_BOOL );
     var_Set( p_playlist, "video-on-top", newval );
 
-    pl_Release( p_playlist );
+    pl_Release( p_this );
     return VLC_SUCCESS;
 }