NFS: rename nfs_client_kset to nfs_kset

[ Upstream commit 8b18a2ed ]

Be brief and match the subsystem name.  There's no need to distinguish this
kset variable from the server.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Stable-dep-of: 956fd46f ("NFSv4: Fix a state manager thread deadlock regression")
Signed-off-by: Sasha Levin <sashal@kernel.org>