LU-13799 osc: Always set aio in anchor

LU-13799 osc: Always set aio in anchor

We currently do not set csi_aio for DIO and use this to
control when we free the aio struct.  (For AIO, we must
free it in cl_sync_io_note, but for other users, we have to
wait until after cl_sync_io_wait has been called.)

The lack of csi_aio causes trouble for the implementation
of the next patch, so instead we always set it and control
freeing by checking at that time if we are doing DIO.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I2122a6a2dad33179e9114494b53c09d0b64f0fa6
Reviewed-on: https://review.whamcloud.com/44153
Reviewed-by: Wang Shilong <wangshilong1991@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>