[gtk+] docs: Fix copy-paste error in gtk_file_chooser_get_extra_widget() doc comment

[Robert Ancell <rancell src gnome org>]

commit 4047a2f53e197bdafeb5fed344bded6a404bc654
Author: Robert Ancell <robert ancell canonical com>
Date:   Sat May 20 13:07:05 2017 +1200

    docs: Fix copy-paste error in gtk_file_chooser_get_extra_widget() doc comment

 gtk/gtkfilechooser.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkfilechooser.c b/gtk/gtkfilechooser.c
index 35de3b3..8463ce4 100644
--- a/gtk/gtkfilechooser.c
+++ b/gtk/gtkfilechooser.c
@@ -1829,7 +1829,7 @@ gtk_file_chooser_set_extra_widget (GtkFileChooser *chooser,
  * gtk_file_chooser_get_extra_widget:
  * @chooser: a #GtkFileChooser
  *
- * Gets the current preview widget; see
+ * Gets the current extra widget; see
  * gtk_file_chooser_set_extra_widget().
  *
  * Returns: (nullable) (transfer none): the current extra widget, or %NULL