Downgrade logging level for not finding a permission in DPGP.

The system apps being granted all permissions may request a permission
that doesn't exist, but that's fine and they just won't get it (e.g.
they requested a car permission on phone), so downgrade the log to be a
warning.

Bug: 181269159
Test: presubmit
Change-Id: I18a2f65d336c0e8414704c91a24329180d7e9752