LU-13490 lustre: fix to make jobstats work for async ra

LU-13490 lustre: fix to make jobstats work for async ra

We use workqueue to triger async readahead, this will make
the problem that read jobstats are not accounted by real
IO, we could fix this by overwritting jobid which inited in
vvp_io_init().

Change-Id: I20b00b17f7a90cf94f1e5be54f47aee8ea2e5440
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Reviewed-on: https://review.whamcloud.com/38426
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Ben Evans <beevans@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>