Refactor cookie members of handshake struct

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_client.c b/library/ssl_client.c
index 0f0ea1d..82695f1 100644
--- a/library/ssl_client.c
+++ b/library/ssl_client.c
@@ -524,8 +524,8 @@
         {
             MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, cookie",
                                    handshake->cookie,
-                                   handshake->verify_cookie_len );
-            cookie_len = handshake->verify_cookie_len;
+                                   handshake->cookie_len );
+            cookie_len = handshake->cookie_len;
         }
 
         MBEDTLS_SSL_CHK_BUF_PTR( p, end, cookie_len + 1 );