[tracker] libtracker-sparql: Add cast to fix compile warning

[Sam Thursfield <sthursfield src gnome org>]

commit ef9ed0435f95c8378ce08c418e4fa7e2ab6fc971
Author: Sam Thursfield <sam afuera me uk>
Date:   Sat May 23 12:29:01 2020 +0200

    libtracker-sparql: Add cast to fix compile warning

 src/libtracker-sparql/tracker-resource.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/libtracker-sparql/tracker-resource.c b/src/libtracker-sparql/tracker-resource.c
index 9f83e440c..003d50f90 100644
--- a/src/libtracker-sparql/tracker-resource.c
+++ b/src/libtracker-sparql/tracker-resource.c
@@ -1838,7 +1838,7 @@ tracker_resource_serialize (TrackerResource *resource)
 
        /* Use a stable sort, so that GVariants are byte compatible */
        properties = tracker_resource_get_properties (resource);
-       properties = g_list_sort (properties, g_strcmp0);
+       properties = g_list_sort (properties, (GCompareFunc) g_strcmp0);
 
        for (l = properties; l; l = l->next) {
                pred = l->data;