core.mk: Add rule for init.usb.rc

Change-Id: I2068c08648aad26bbfb35a6a7890757b5d8b01c9
Signed-off-by: Mike Lockwood <lockwood@google.com>
diff --git a/target/product/core.mk b/target/product/core.mk
index 732e476..62692b9 100644
--- a/target/product/core.mk
+++ b/target/product/core.mk
@@ -112,6 +112,8 @@
     sensorservice \
     lint
 
+PRODUCT_COPY_FILES += \
+    system/core/rootdir/init.usb.rc:root/init.usb.rc \
 
 # host-only dependencies
 ifeq ($(WITH_HOST_DALVIK),true)