dm: scsi: Document and rename the scsi_scan() parameter

The 'mode' parameter is actually a flag to determine whether to display
a list of devices found during the scan. Rename it to reflect this, add a
function comment and adjust callers to use a boolean.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/common/spl/spl_sata.c b/common/spl/spl_sata.c
index 5476206..bac11f6 100644
--- a/common/spl/spl_sata.c
+++ b/common/spl/spl_sata.c
@@ -34,7 +34,7 @@
 		return err;
 	} else {
 		/* try to recognize storage devices immediately */
-		scsi_scan(0);
+		scsi_scan(false);
 		stor_dev = blk_get_devnum_by_type(IF_TYPE_SCSI, 0);
 		if (!stor_dev)
 			return -ENODEV;