[gnome-settings-daemon] common: Fix a compiler warning

[Kalev Lember <klember src gnome org>]

commit 753c48abe68866eb196e8ec70fc90ba9cc3b3dcc
Author: Kalev Lember <klember redhat com>
Date:   Tue Oct 20 11:53:42 2015 +0200

    common: Fix a compiler warning
    
    gsd-input-helper.c: In function ‘trackball_is_present’:
    gsd-input-helper.c:256:18: warning: ‘retval’ may be used uninitialized in this function 
[-Wmaybe-uninitialized]
    
    https://bugzilla.gnome.org/show_bug.cgi?id=756859

 plugins/common/gsd-input-helper.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/plugins/common/gsd-input-helper.c b/plugins/common/gsd-input-helper.c
index 7396d38..e3fe2d8 100644
--- a/plugins/common/gsd-input-helper.c
+++ b/plugins/common/gsd-input-helper.c
@@ -253,7 +253,7 @@ mouse_is_present (void)
 gboolean
 trackball_is_present (void)
 {
-        gboolean retval;
+        gboolean retval = FALSE;
         GList *l, *mice = gsd_device_manager_list_devices (gsd_device_manager_get (),
                                                            GSD_DEVICE_TYPE_MOUSE);
         if (mice == NULL)