I found that if use mutex in `rt_kprintf`,
the `rt_enter_critical` will create a assert
error later. after chehcking,I found all
operation with fd_table has using
`dfs_lock/unlock` to protect. so I think
using `dfs_lock` is enough. thanks.
Signed-off-by: a1012112796 <1012112796@qq.com>