Fix that Bluetooth device should not duplicate in the list

This CL before, if someone call addDevice() twice to add
same device and previous addDevice() call is synchronized,
it will cause list have duplicate device.
Because addDevice() will add device directly without check
whether device already in the list.

This CL is add duplicate check in addDevice().

Bug: 139516941
Test:  make -j42 RunSettingsLibRoboTests
Change-Id: I859067048c71be95b0a3b2ff0317ea93f49cea7d