Floss: Improve the logging in finding HCI interface

The error message was mistakenly logged in success case. This fixes it
and also includes the number of index found into the message to help
future debugging.

Bug: 357792559
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: manually
Flag: EXEMPT, Floss-only changes

Change-Id: I519ffa09ae3ebee3b08849ac030641d5b9d90ee0