nfsd: use new wake_up_var interfaces.

The wake_up_var interface is fragile as barriers are sometimes needed.
There are now new interfaces so that most wake-ups can use an interface
that is guaranteed to have all barriers needed.

This patch changes the wake up on cl_cb_inflight to use
atomic_dec_and_wake_up().

It also changes the wake up on rp_locked to use store_release_wake_up().
This involves changing rp_locked from atomic_t to int.

Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>