Replace get current tcb method from nxsched_get_tcb(nxsched_gettid()) to this_task(),
change two function calls with inline function to improve performance:
FAR struct tcb_s *tcb = nxsched_get_tcb(nxsched_gettid());
FAR struct tcb_s *tcb = this_task();
Signed-off-by: chao an <anchao.archer@bytedance.com>
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