LU-9633 obdclass: Add kernel doc style for obdclass/cl_io.c

LU-9633 obdclass: Add kernel doc style for obdclass/cl_io.c

This patch converts existing functional comments
to kernel doc style comments and removes '/**' for
comments which is not meant to be a kernel-doc comment

Test-Parameters: trivial
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: Ib0a8bc3bdef68a6e894a683f4d79396f081eff61
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58415
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Petros Koutoupis <petros.koutoupis@hpe.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Anjus George <georgea@ornl.gov>
Reviewed-by: Oleg Drokin <green@whamcloud.com>