LU-17848 dt: cleanup dt_object.h header

LU-17848 dt: cleanup dt_object.h header

Cleanup a number of LASSERT statements to unify style.

Use kernel doc style instead of the old Doxygen style. Avoid
using ** for comments that aren't kernel doc.

Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: Ia23492534a05bce4850ca38ab7c06a07000504d3
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55126
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: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>