omni: use DEVICE_PACKAGE_OVERLAYS for proper layering of overlays

Change-Id: I1cbe0704471d8d2ca0675e0ed861251a41a91ec7
diff --git a/utils/emulator/common.mk b/utils/emulator/common.mk
index 5949d9d..11c725c 100644
--- a/utils/emulator/common.mk
+++ b/utils/emulator/common.mk
@@ -70,6 +70,6 @@
 -include vendor/omni/config/version.mk
 
 # Add our overlays
-PRODUCT_PACKAGE_OVERLAYS += vendor/omni/overlay/common
+DEVICE_PACKAGE_OVERLAYS += vendor/omni/overlay/common
 
 WITH_DEXPREOPT := false