Use unchecked admin lookup for getStorageEncryption()

Due to a copy/paste typo, getStorageEncryption() was protected by
getActiveAdminForCallerLocked(), which made the API unreadable if the
caller is not an admin.  This doesn't match the rest of the DPM API which
allows the "get" calls to be made anonymously.

This fix supercedes the proposed workaround CL in the DPM ApiDemo sample.

Change-Id: If1a6237634e97ced09a7c6a8876bb6b0f60c9be9