scsi: scsi_transport_sas: don't bounce highmem pages for the smp handler

All three instance of ->smp_handler deal with highmem backed requests
just fine.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>