LU-15901 mdc: Remove entry from list before freeing

LU-15901 mdc: Remove entry from list before freeing

mdc_changelog_cdev_init forgot to remove entries from list if
chardev allocation failed

Lustre-change: https://review.whamcloud.com/47480
Lustre-commit: 441ec2296a0938dd30cf60a70943eb0799d1d70c

Change-Id: Ic76b5320bf80c7f7f60c7682bda4bc37a0b300bd
Fixes: d0423abc1ad ("LU-12506 changelog: support large number of MDT")
Signed-off-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/47783
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>