scsi: Do not rely on blk-mq for double completions

scsi: Do not rely on blk-mq for double completions

The scsi timeout error handling had been directly updating the block
layer's request state to prevent a error handling and a natural completion
from completing the same request twice. Fix this layering violation
by having scsi control the fate of its commands with scsi owned flags
rather than use blk-mq's.

Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Keith Busch <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>