scsi: libata: Fix the ata_scsi_dma_need_drain stub

We not only need the stub when libata is disabled, but also if it is
modular and there are built-in SAS drivers (which can happen when
SCSI_SAS_ATA is disabled).

Link: https://lore.kernel.org/r/20200620071302.462974-2-hch@lst.de
Fixes: b8f1d1e0

 ("scsi: Wire up ata_scsi_dma_need_drain for SAS HBA drivers")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>