[poll][select] 修复select死循环的问题 (#5740)

components/libc/posix/io/poll/poll.c

@@ -168,6 +168,7 @@ static int poll_do(struct pollfd *fds, nfds_t nfds, struct rt_poll_table *pt, in
     {
         pf = fds;
         num = 0;
+        pt->triggered = 0;
 
         for (n = 0; n < nfds; n ++)
         {