scsi: push blk_status_t up into scsi_setup_{fs,scsi}_cmnd

This just moves the prep_to_mq calls up in preparation of further removal
of BLKPREP_* usage.

Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>