nvme: fix compilation of scsi component

Since we moved the cdb parts and define out of the block proper,
we need to include scsi/scsi_request.h for the nvme scsi layer.

Fixes: 82ed4db4 ("block: split scsi_request out of struct request")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jens Axboe <axboe@fb.com>