bass: Avoid double add of devices from group

When group operation flag is set there is possibility that second device
from set would not have cached metadata. This change correct caching
place to internal loop iterating over set devices.

Tag: #feature
Test: atest LeAudioServiceTest LeAudioBroadcastServiceTest
Bug: 298080973
Bug: 308171251
Change-Id: Iab45ce3d06cf845e3ba3036eec3e5ad280a0006b