AudioDeviceInventory: fix LE Audio Broadcast device name.

Make sure a non empty device name is provided for LE Audio broadcast
devices as the this is needed for proper MediaRouter operation.
The device name is not provided by th eBT stack for broadcast devices.

Bug: 290701463
Test: make
Change-Id: Ibe34660d589b18a1801cb51efd87822c33c822b0