greybus: nullify dangling pointers

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/staging/greybus/ap.c

@@ -367,6 +367,7 @@ int gb_ap_init(void)
 void gb_ap_exit(void)
 {
 	destroy_workqueue(ap_workqueue);
+	ap_workqueue = NULL;
 }
 
 

drivers/staging/greybus/debugfs.c

@@ -26,4 +26,5 @@ int gb_debugfs_init(void)
 void gb_debugfs_cleanup(void)
 {
 	debugfs_remove_recursive(gb_debug_root);
+	gb_debug_root = NULL;
 }

drivers/staging/greybus/gbuf.c

@@ -136,4 +136,5 @@ int gb_gbuf_init(void)
 void gb_gbuf_exit(void)
 {
 	kmem_cache_destroy(gbuf_head_cache);
+	gbuf_head_cache = NULL;
 }