dm: scsi: Adjust return value of scsi_exec()

Change this function to return an error number instead of true/false.
This allows us to return a proper error number.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 5a20b97..3528a1f 100644
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -960,14 +960,14 @@
 		break;
 	default:
 		printf("Unsupport SCSI command 0x%02x\n", pccb->cmd[0]);
-		return false;
+		return -ENOTSUPP;
 	}
 
 	if (ret) {
 		debug("SCSI command 0x%02x ret errno %d\n", pccb->cmd[0], ret);
-		return false;
+		return ret;
 	}
-	return true;
+	return 0;
 
 }