block/block-backend: blk_iostatus_reset: drop usage of bs->job

block/block-backend: blk_iostatus_reset: drop usage of bs->job

We are going to remove bs->job pointer. Drop it's usage in
blk_iostatus_reset.

blk_iostatus_reset() has only two callers:

1. blk_attach_dev(). This doesn't have anything to do with jobs and
    attaching a new guest device won't solve any problem the job
    encountered, so no reason to reset the iostatus for the job.

2. qmp_cont(). This resets the iostatus for everything. We can just
    call block_job_iostatus_reset() for all block jobs instead of going
    through BlockBackend.

Suggested-by: Kevin Wolf <[email protected]>
Signed-off-by: Vladimir Sementsov-Ogievskiy <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>