Update comment to use CAS-specific error codes

    // associated MediaCas session is used to load decryption keys

    // into the crypto/cas plugin.  The keys are then referenced by key-id

    // in the 'key' parameter to the decrypt() method.

    // Should return NO_ERROR on success, ERROR_DRM_SESSION_NOT_OPENED if

    // Should return NO_ERROR on success, ERROR_CAS_SESSION_NOT_OPENED if

    // the session is not opened and a code from MediaErrors.h otherwise.

    virtual status_t setMediaCasSession(const CasSessionId& sessionId) = 0;

    // If the error returned falls into the range

    // ERROR_DRM_VENDOR_MIN..ERROR_DRM_VENDOR_MAX, errorDetailMsg should be

    // ERROR_CAS_VENDOR_MIN..ERROR_CAS_VENDOR_MAX, errorDetailMsg should be

    // filled in with an appropriate string.

    // At the java level these special errors will then trigger a

    // MediaCodec.CryptoException that gives clients access to both