scsi-disk: add data direction checking

scsi_req_parse() already provides for a data direction setting,
so we should be using it to check for correct direction.
And we should return the sense code 'INVALID FIELD IN CDB'
in these cases.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
