pass in correct buffer to print_id

hdr.id is actually larger than sha

Change-Id: Iac33dbaaf4bea9acde5ba49d8601f7ac767677d5
diff --git a/mkbootimg/mkbootimg.c b/mkbootimg/mkbootimg.c
index 1a6e4cd..40e5261 100644
--- a/mkbootimg/mkbootimg.c
+++ b/mkbootimg/mkbootimg.c
@@ -283,7 +283,7 @@
     }
 
     if (get_id) {
-        print_id(sha, sizeof(hdr.id));
+        print_id((uint8_t *) hdr.id, sizeof(hdr.id));
     }
 
     return 0;