As we only set BLOCKED status in context switch_out, which means, only
running thread can be changed to BLOCKED, but runnable thread can not.
This lead to the deadloop in sleep_thread_sync.
To solve the problem, in sleep_thread, we set the status to BLOCKED
directly when the original thread status is RUNNABLE.
Tracked-On: #5115
Signed-off-by: Conghui Chen <conghui.chen@intel.com>