LU-14070 tgt: check obd_recovering in tgt_brw_unlock()

LU-14070 tgt: check obd_recovering in tgt_brw_unlock()

Since tgt_brw_lock() never takes a lock during recovery,
the tgt_brw_unlock() should check that also to prevent
false-positive triggering of assertion.

Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Change-Id: Ic6b6f6fa16678622460101d26df14f523e56a47a
Reviewed-on: https://review.whamcloud.com/40382
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>