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

[Sébastien Wilmet <swilmet src gnome org>]

commit 7ae55f79dd71a76c64c3ce28368cd6d02d66a862
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Thu May 10 21:31:23 2018 +0200

    MarksSequence: fix compil warning (-Wcast-function-type)

 gtksourceview/gtksourcemarkssequence.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/gtksourceview/gtksourcemarkssequence.c b/gtksourceview/gtksourcemarkssequence.c
index 92126c2..9678efd 100644
--- a/gtksourceview/gtksourcemarkssequence.c
+++ b/gtksourceview/gtksourcemarkssequence.c
@@ -81,7 +81,8 @@ free_sequence (GtkSourceMarksSequence *seq)
 
 static gint
 compare_marks (GtkTextMark *mark1,
-              GtkTextMark *mark2)
+              GtkTextMark *mark2,
+              gpointer     user_data)
 {
        GtkTextBuffer *buffer;
        GtkTextIter iter1;