part: mac: Suppress the error message after reading ddb

Change to use 'debug' to output the error message if it fails to
read the driver descriptor block.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

disk/part_mac.c

@@ -159,15 +159,11 @@ static int part_mac_read_ddb(struct blk_desc *dev_desc,
 			     mac_driver_desc_t *ddb_p)
 {
 	if (blk_dread(dev_desc, 0, 1, (ulong *)ddb_p) != 1) {
-		printf("** Can't read Driver Descriptor Block **\n");
+		debug("** Can't read Driver Descriptor Block **\n");
 		return (-1);
 	}
 
 	if (ddb_p->signature != MAC_DRIVER_MAGIC) {
-#if 0
-		printf ("** Bad Signature: expected 0x%04x, got 0x%04x\n",
-			MAC_DRIVER_MAGIC, ddb_p->signature);
-#endif
 		return (-1);
 	}
 	return (0);