LU-15308 lod: set ldo_mirrors to NULL on error

LU-15308 lod: set ldo_mirrors to NULL on error

In lod_alloc_comp_entries() if OBD_ALLOC_LARGE fails and we free
ldo_mirrors then we set it to NULL to avoid a double free later.

Lustre-change: https://review.whamcloud.com/47008
Lustre-commit: 26f6b0e952b24de2a900f6f1eeae79fea6af4787

Test-Parameters: trivial
Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: I27552d1eaecc06720190db9cfe89ded71b9fef53
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/47850
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>