NFS: Get rid of the unneeded addr stored in callback arguments

Commit c36fca52 "NFS refactor nfs_find_client and reference client
across callback processing" has store clp in cb_process_state
which is set in cb_sequence.

So that, it's unneeded to store address pointer in any callback arguments.

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>