floss: Always copy bonded devices

This removes guard num_devices > 0, otherwise there is a bug where we
failed to set the property length to 0 and got uninitialized data
instead.

Bug: 207116922
Tag: #floss
Test: Call `list bonded` on btclient

Change-Id: I3886ed033e1710ff1400ef57dc6b6d53502cd673