LU-16796 libcfs: Change struct cfs_hash to use kref

LU-16796 libcfs: Change struct cfs_hash to use kref

This patch changes struct cfs_hash to use
kref(refcount_t) instead of atomic_t

Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I58b5e8311a34b3b128c1440b93958389b0fcdd48
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51938
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>