Fix a gcc warning about possible fall through

Reviewed-by: NTim Hudson <tjh@openssl.org>
Reviewed-by: NKurt Roeckx <kurt@roeckx.be>
(Merged from https://github.com/openssl/openssl/pull/5373)

test/handshake_helper.c

@@ -1155,6 +1155,7 @@ static handshake_status_t handshake_status(peer_status_t last_status,
              */
             return INTERNAL_ERROR;
         }
+        break;
 
     case PEER_RETRY:
         return HANDSHAKE_RETRY;