[gnome-control-center/gnome-3-30] object-cache: Declare singleton instance as static

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 4002b06f3a0e4867bf86c659b5f323f91710b141
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Tue Sep 25 20:45:12 2018 -0300

    object-cache: Declare singleton instance as static
    
    Otherwise, it is visible for other compile units. This
    is a theoretical problem though, there's nothing wrong
    happening right now.

 shell/cc-object-storage.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/shell/cc-object-storage.c b/shell/cc-object-storage.c
index 3e3ab4d9a..7aeafb1fd 100644
--- a/shell/cc-object-storage.c
+++ b/shell/cc-object-storage.c
@@ -30,7 +30,7 @@ struct _CcObjectStorage
 G_DEFINE_TYPE (CcObjectStorage, cc_object_storage, G_TYPE_OBJECT)
 
 /* Singleton instance */
-CcObjectStorage *_instance = NULL;
+static CcObjectStorage *_instance = NULL;
 
 /* GTask API to create a new D-Bus proxy */
 typedef struct