zeppelin: cyanogen_zeppelin.mk: sysctl.conf is not being copied

The file system/etc/sysctl.conf is ending up empty.  It does not contain the contents of device/motorola/zeppelin/sysctl.conf like it should.  A user on the M3 forum suggested this change.  Please approve this change if it will lead to the sysctl.conf file being copied correctly.
Submitted on behalf of a third-party: User 'epinter' from the M3 forums.

Change-Id: Ia1222f10138b8dd06662cddc25a8168f21d61f50

products/cyanogen_zeppelin.mk

@@ -39,6 +39,9 @@ PRODUCT_BUILD_PROP_OVERRIDES += PRODUCT_NAME=zeppelin TARGET_DEVICE=zeppelin BUI
 PRODUCT_COPY_FILES +=  \
     vendor/cyanogen/prebuilt/mdpi/media/bootanimation.zip:system/media/bootanimation.zip
 
+PRODUCT_COPY_FILES += \
+    device/motorola/zeppelin/sysctl.conf:system/etc/sysctl.conf
+
 PRODUCT_PACKAGE_OVERLAYS += vendor/cyanogen/overlay/zeppelin
 
 # Add the FM app