LU-16154 obdclass: free inst_name correctly

LU-16154 obdclass: free inst_name correctly

In functon class_config_llog_handler(), inst_name should be freed
correctly before break.

Signed-off-by: Emoly Liu <emoly@whamcloud.com>
Change-Id: I6adc0ed62c3c637237834b799f25666d0e7e1ecb
Reviewed-on: https://review.whamcloud.com/48542
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Zhenyu Xu <bobijam@hotmail.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>