[gtksourceview] CompletionWordsLibrary: fix compil warning (-Wcast-function-type)

[Sébastien Wilmet <swilmet src gnome org>]

commit 8fb1231b9d88ea25faf6d57a043b7d31adfb6855
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Thu May 10 20:53:34 2018 +0200

    CompletionWordsLibrary: fix compil warning (-Wcast-function-type)
    
    This warning is enabled by -Wextra.

 .../words/gtksourcecompletionwordslibrary.c        |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/gtksourceview/completion-providers/words/gtksourcecompletionwordslibrary.c 
b/gtksourceview/completion-providers/words/gtksourcecompletionwordslibrary.c
index 71ba2ee..0c49405 100644
--- a/gtksourceview/completion-providers/words/gtksourcecompletionwordslibrary.c
+++ b/gtksourceview/completion-providers/words/gtksourcecompletionwordslibrary.c
@@ -94,7 +94,8 @@ gtk_source_completion_words_library_new (void)
 
 static gint
 compare_full (GtkSourceCompletionWordsProposal *a,
-             GtkSourceCompletionWordsProposal *b)
+             GtkSourceCompletionWordsProposal *b,
+             gpointer                          user_data)
 {
        if (a == b)
        {