SUNRPC: do not fail gss proc NULL calls with EACCES

Otherwise RPCSEC_GSS_DESTROY messages are not sent.
Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/auth_gss/auth_gss.c

@@ -1517,7 +1517,7 @@ gss_refresh(struct rpc_task *task)
 static int
 gss_refresh_null(struct rpc_task *task)
 {
-	return -EACCES;
+	return 0;
 }
 
 static __be32 *