Suppress unsafe cast warning

Change-Id: I4eba78d0ec79354e17acfc9d1b42c558b1735259
diff --git a/src/main/java/com/android/tools/r8/graph/GraphLens.java b/src/main/java/com/android/tools/r8/graph/GraphLens.java
index a69be5e..eec753e 100644
--- a/src/main/java/com/android/tools/r8/graph/GraphLens.java
+++ b/src/main/java/com/android/tools/r8/graph/GraphLens.java
@@ -502,6 +502,7 @@
     return result;
   }
 
+  @SuppressWarnings("unchecked")
   public <T extends DexReference> T rewriteReference(T reference) {
     if (reference.isDexField()) {
       return (T) getRenamedFieldSignature(reference.asDexField());