mysqltest: use do_stmt_close() not mysql_stmt_close()

do_stmt_close() is embedded-aware.

this fixes the failure of innodb.innodb_bug48024 --ps --embed

client/mysqltest.cc

@@ -1418,7 +1418,7 @@ void close_statements()
   for (con= connections; con < next_con; con++)
   {
     if (con->stmt)
-      mysql_stmt_close(con->stmt);
+      do_stmt_close(con);
     con->stmt= 0;
   }
   DBUG_VOID_RETURN;