crypt_algo: add needed include

gcc11 flags an error on this missing include

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: I9eb8c1d9f1427b56e71d4103ae402980075f0780
diff --git a/crypt_algo.hpp b/crypt_algo.hpp
index 366f2b0..f4d7363 100644
--- a/crypt_algo.hpp
+++ b/crypt_algo.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <array>
+#include <cstddef>
 #include <cstdint>
 #include <vector>