LU-14132 lod: do not initialize sub llogs twice

LU-14132 lod: do not initialize sub llogs twice

this can happen during MDT re-activation and then result in leaked
objects:
lod_device_free()) ASSERTION( atomic_read(&lu->ld_ref) == 0 )

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I0afb335ffb20532f9171dd2e514100b12f4d9a76
Reviewed-on: https://review.whamcloud.com/40605
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>