LU-13814 llite: note references in direct_rw_pages

LU-13814 llite: note references in direct_rw_pages

Add a comment denoting the function of cl_2queue_fini in
ll_direct_rw_pages.  This will eventually be removed as
part of this process, but this comment serves as a remidner
for when we get to that step.

Test-Parameters: trivial
Signed-off-by: Patrick Farrell <patrick.farrell@oracle.com>
Change-Id: I98a03c7ee0d97665d77a321bc21b4fab6448b2d7
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/52083
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Qian Yingjin <qian@ddn.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>