LU-16796 lfsck: Change lfsck_instance to use refcount_t

LU-16796 lfsck: Change lfsck_instance to use refcount_t

This patch changes struct lfsck_instance to use
refcount_t instead of atomic_t

Test-Parameters: trivial testlist=sanity-lfsck
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I9bf3337ed7b68dbd44e723bf7c1374a8e3a07eb7
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56195
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>