nfs: Drop bad comment in nfs41_walk_client_list()

Commit 7b1f1fd1

 "NFSv4/4.1: Fix bugs in nfs4[01]_walk_client_list"
have change the logical of the list_for_each_entry().

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