floss: Don't assert when failing to SaveImmediately

Floss prefers to log an error instead of crashing.

Bug: 308721592
Tag: #floss
Test: mmm packages/modules/Bluetooth
Flag: EXEMPT, floss change for ChromeOS only.
Change-Id: I49b0ed6228fc3a34fadef5529a7d58a1fba421b3