Use full path for sepolicy finalization script

Otherwise we can only run main script from ANDROID_BUILD_TOP

Ignore-AOSP-First: b/304316873#comment10

https://android-build.corp.google.com/builds/abtd/run/L79300030001797715

Test: ./finalize-vintf-resources.sh
Bug: none
Change-Id: Id9a8c27b9ceb6741c0990d2189bb555d1f60c89d