NFS: fix the return value check by using IS_ERR

In case of error, the function rpcauth_create() returns ERR_PTR()
and never returns NULL pointer. The NULL test in the return value
check should be replaced with IS_ERR().

dpatch engine is used to auto generated this patch.
(https://github.com/weiyj/dpatch)
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4namespace.c

@@ -205,7 +205,7 @@ struct rpc_clnt *nfs4_create_sec_client(struct rpc_clnt *clnt, struct inode *ino
 		return clone;
 
 	auth = rpcauth_create(flavor, clone);
-	if (!auth) {
+	if (IS_ERR(auth)) {
 		rpc_shutdown_client(clone);
 		clone = ERR_PTR(-EIO);
 	}

fs/nfs/nfs4proc.c

@@ -2399,7 +2399,7 @@ static int nfs4_lookup_root_sec(struct nfs_server *server, struct nfs_fh *fhandl
 	int ret;
 
 	auth = rpcauth_create(flavor, server->client);
-	if (!auth) {
+	if (IS_ERR(auth)) {
 		ret = -EIO;
 		goto out;
 	}