libata: fix DMA to stack in reading devslp_timing parameters

Commit 803739d2 ("[libata] replace
sata_settings with devslp_timing"), which was also Cc: stable, used a
stack buffer to receive data from ata_read_log_page(), which triggers
the following warning:
 ahci 0000:00:1f.2: DMA-API: device driver maps memory fromstack [addr=ffff880140469948]

Fix this by using ap->sector_buf instead of a stack buffer.
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Cc: stable@kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/libata-core.c

@@ -2329,7 +2329,7 @@ int ata_dev_configure(struct ata_device *dev)
 		 * from SATA Settings page of Identify Device Data Log.
 		 */
 		if (ata_id_has_devslp(dev->id)) {
-			u8 sata_setting[ATA_SECT_SIZE];
+			u8 *sata_setting = ap->sector_buf;
 			int i, j;
 
 			dev->flags |= ATA_DFLAG_DEVSLP;