liboverlay: remove warnings during compilation

- Remove unused variables
- Use proper typecast

Change-Id: Ia60fc4c3c7ec39a1df4a780de7f5d75d723f7960
diff --git a/liboverlay/overlayMdssRot.cpp b/liboverlay/overlayMdssRot.cpp
index c6d5332..083e507 100644
--- a/liboverlay/overlayMdssRot.cpp
+++ b/liboverlay/overlayMdssRot.cpp
@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2008 The Android Open Source Project
- * Copyright (c) 2010-2013, The Linux Foundation. All rights reserved.
+ * Copyright (c) 2010-2014, The Linux Foundation. All rights reserved.
  * Not a Contribution, Apache license notifications and license are retained
  * for attribution purposes only.
  *
@@ -92,7 +92,8 @@
     mRotInfo.dst_rect.h = crop.h;
 }
 
-void MdssRot::setDownscale(int ds) {}
+void MdssRot::setDownscale(int /*ds*/) {
+}
 
 void MdssRot::setFlags(const utils::eMdpFlags& flags) {
     mRotInfo.flags = flags;