Hardware Composer add const for handle pointer

Change-Id: Icf53be12ed43bce19b152fa7f1dee104d713b8da
diff --git a/include/hardware/hwcomposer.h b/include/hardware/hwcomposer.h
index 9a7149a..1e5779c 100644
--- a/include/hardware/hwcomposer.h
+++ b/include/hardware/hwcomposer.h
@@ -148,7 +148,7 @@
 
     /* handle of buffer to compose. this handle is guaranteed to have been
      * allocated with gralloc */
-    native_handle_t* handle;
+    const native_handle_t* handle;
 
     /* transformation to apply to the buffer during composition */
     uint32_t transform;