nfsd: fix clp->cl_revoked list deletion causing softlock in nfsd

commit 2d4a532d ("nfsd: ensure that clp->cl_revoked list is
protected by clp->cl_lock") removed the use of the reaplist to
clean out clp->cl_revoked. It failed to change list_entry() to
walk clp->cl_revoked.next instead of reaplist.next

Fixes: 2d4a532d ("nfsd: ensure that clp->cl_revoked list is protected by clp->cl_lock")
Cc: stable@vger.kernel.org
Reported-by: Eric Meddaugh <etmsys@rit.edu>
Tested-by: Eric Meddaugh <etmsys@rit.edu>
Signed-off-by: Andrew Elble <aweits@rit.edu>
Reviewed-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>