Set dtc as dependency of dtdiff

Change-Id: I7e5e604ff5b760210a3d615d4b4a0b0d9e04fc9a
Test: T/H
diff --git a/Android.bp b/Android.bp
index b20b802..f9f2334 100644
--- a/Android.bp
+++ b/Android.bp
@@ -122,6 +122,7 @@
 sh_binary_host {
     name: "dtdiff",
     src: "dtdiff",
+    required: ["dtc"],
 }
 
 genrule {