Update to commit 6c757e9f ("docs/scheduler:
fix unit error")

ddb21d27 ("docs/scheduler: Change unit of
cpu_time and rq_time to nanoseconds")
Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Wu XiangCheng <bobwxc@email.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/3cb1c4c466dfa38d72a867dc6e2c833ceb69ecb7.1658983157.git.siyanteng@loongson.cnSigned-off-by: Jonathan Corbet <corbet@lwn.net>