LU-18056 osp: fix KASAN warning when lu2dt_dev() lwp device

LU-18056 osp: fix KASAN warning when lu2dt_dev() lwp device

A lwp device isn't really a dt device, so it shouldn't be
marked as such. This causes a KASAN warning when obd_setup()
attempts to access dt device fields using lu2dt_dev():

 BUG: KASAN: slab-out-of-bounds in obd_setup+0x208/0x4b0 [obdclass]

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: Ib52b0f93c35a7d966314b6375ee963bc59f86abb
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55825
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>