LU-8807 llite: check reply status in ll_migrate()

LU-8807 llite: check reply status in ll_migrate()

ll_migrate() should check reply status before trying to read
reply buffer, checking if request is NULL doesn't make sense.

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: I585844e0c1118fad23f19791dc95e34bc0d6e38a
Reviewed-on: https://review.whamcloud.com/23666
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>