Fix typo from previous commit.

core_dex2oat_dependency has a '|' dependency, so we should do :=
instead of += to force recompilation of the image.

Change-Id: Ic59b86666fa69038a67459e7be11c57c20bf815b
diff --git a/build/Android.oat.mk b/build/Android.oat.mk
index d71ae29..3272c27 100644
--- a/build/Android.oat.mk
+++ b/build/Android.oat.mk
@@ -177,7 +177,9 @@
   endif
   ifeq ($(1),optimizing)
     core_compile_options += --compiler-backend=Optimizing
-    core_dex2oat_dependency += $(DEX2OAT)
+    # With the optimizing compiler, we want to rerun dex2oat whenever there is
+    # a dex2oat change to catch regressions early.
+    core_dex2oat_dependency := $(DEX2OAT)
     core_infix := -optimizing
   endif
   ifeq ($(1),interpreter)