Skip legacy-fs-verity setup if file already has it

Test: 1. put com.foo.apk in /system/priv-app
      2. adb install-multiple -r -p com.foo split.apk
      3. adb install-multiple -r -p com.foo split.apk (second time, only
         succeed with this change)
Test: update a priv app (no regression)
Bug: 129509604
Change-Id: I591dd4504e3ba6f1499ebd045dc4f1adbd88d4e3