LU-15038 mgc: release cl_mgc_mutex on error

LU-15038 mgc: release cl_mgc_mutex on error

If local_oid_storage_init() returns an error, the cl_mgc_mutex()
should be released.

Fixes: 3e38436dc09 ("LU-2059 llog: MGC to use OSD API for backup logs")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I921dde4e9202733874d8e7f980e95af23739a655
Reviewed-on: https://review.whamcloud.com/45063
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>