percpu-refcount: add __must_check to percpu_ref_init() and don't use ACCESS_ONCE...

Two small changes.

* Unlike most init functions, percpu_ref_init() allocates memory and
  may fail.  Let's mark it with __must_check in case the caller
  forgets.

* percpu_ref_kill_rcu() is unnecessarily using ACCESS_ONCE() to
  dereference @ref->pcpu_count, which can be misleading.  The pointer
  is guaranteed to be valid and visible and can't change underneath
  the function.  Drop ACCESS_ONCE().

Signed-off-by: Tejun Heo <tj@kernel.org>

diff --cc include/linux/percpu-refcount.h
Simple merge

diff --cc lib/percpu-refcount.c
Simple merge