nfsd: Fix bad reserving space for encoding rdattr_error

Introduced by commit 561f0ed498 (nfsd4: allow large readdirs).

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 2fc7abe..b56b1cc0 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -2641,7 +2641,7 @@
 {
 	__be32 *p;
 
-	p = xdr_reserve_space(xdr, 6);
+	p = xdr_reserve_space(xdr, 20);
 	if (!p)
 		return NULL;
 	*p++ = htonl(2);