Correct processing of AES-SHA stitched ciphers

Fixes: #15706

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15740)

providers/implementations/ciphers/cipher_aes_cbc_hmac_sha256_hw.c

@@ -733,7 +733,7 @@ static int aesni_cbc_hmac_sha256_set_tls1_aad(void *vctx,
             if (len < AES_BLOCK_SIZE)
                 return 0;
             len -= AES_BLOCK_SIZE;
-            p[aad_len] = len >> 8;
+            p[aad_len - 2] = len >> 8;
             p[aad_len - 1] = len;
         }
         sctx->md = sctx->head;