fs/vfs: result_independent_of_operands

timeout is a type of int
in MSEC2TICK, timeout may be multiplied by USEC_PER_MSEC
and the result may be out of range of int
Besides, this will induce following ERROR while running simulator:
vfs/fs_poll.c:498:38: runtime error: signed integer overflow:
19768268 * 1000 cannot be represented in type 'int'

Signed-off-by: zhengyu9 <zhengyu9@xiaomi.com>
Signed-off-by: ligd <liguiding1@xiaomi.com>

fs/vfs/fs_poll.c

@@ -495,7 +495,7 @@ int poll(FAR struct pollfd *fds, nfds_t nfds, int timeout)
            * will return immediately.
            */
 
-          ret = nxsem_tickwait(&sem, MSEC2TICK(timeout));
+          ret = nxsem_tickwait(&sem, MSEC2TICK((clock_t)timeout));
           if (ret < 0)
             {
               if (ret == -ETIMEDOUT)