This is a micro optimazation for a hot path.

- We don't need to check if @CA returned from task_ca() is NULL.
- We don't need to check if @CA returned from parent_ca() is NULL.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/515536B7.6060602@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>