dm: ahci: Correct uclass private data

This is expected to be attached to the uclass and the code operates that
way, but the uclass has not been updated. Fix it to avoid using memory at
address 0.

Signed-off-by: Simon Glass <sjg@chromium.org>
Fixes: 47fc61a (dm: ahci: Drop use of probe_ent)

drivers/ata/ahci-uclass.c

@@ -6,9 +6,11 @@
  */
 
 #include <common.h>
+#include <ahci.h>
 #include <dm.h>
 
 UCLASS_DRIVER(ahci) = {
 	.id		= UCLASS_AHCI,
 	.name		= "ahci",
+	.per_device_auto_alloc_size = sizeof(struct ahci_uc_priv),
 };

drivers/ata/ahci.c

@@ -935,7 +935,7 @@ static int ahci_scsi_exec(struct udevice *dev, struct scsi_cmd *pccb)
 {
 	struct ahci_uc_priv *uc_priv;
 #ifdef CONFIG_DM_SCSI
-	uc_priv = dev_get_uclass_priv(dev);
+	uc_priv = dev_get_uclass_priv(dev->parent);
 #else
 	uc_priv = probe_ent;
 #endif