LU-4461 mdt: correct test in mdt_seq_fini_cli()

LU-4461 mdt: correct test in mdt_seq_fini_cli()

In mdt_seq_fini_cli() pass ss->ss_server_seq to seq_server_set_cli()
if it's *not* NULL.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I494219416b772a33838dd4fb9303d6b9519050f9
Reviewed-on: http://review.whamcloud.com/8786
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>