ceph: add missing #includes

Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/auth_none.h b/fs/ceph/auth_none.h
index 56c0553..8164df1 100644
--- a/fs/ceph/auth_none.h
+++ b/fs/ceph/auth_none.h
@@ -1,6 +1,8 @@
 #ifndef _FS_CEPH_AUTH_NONE_H
 #define _FS_CEPH_AUTH_NONE_H
 
+#include <linux/slab.h>
+
 #include "auth.h"
 
 /*