LU-18049 obdclass: fix class_add_nids_to_uuid

LU-18049 obdclass: fix class_add_nids_to_uuid

Store nid in un_nids array beginning from the
0-element. Without the patch it starts from
the 1st element because a counter is incremented
before copying.

Fixes: e4d2d4ff74 ("LU-13306 mgc: handle large NID formats")
Signed-off-by: Sergey Cheremencev <scherementsev@ddn.com>
Change-Id: I257825de515b083df6af8b8f3ab784b48074a1fe
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56499
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>