LeAudio: Fix unable to configure getting ready devices

If devices are still getting ready, we will try to configure them
and fail.

With this change we will configure only the fully connected devices.

Bug: 271941416
Tag: #feature
Test: atest --host bluetooth_le_audio_test --no-bazel-mode
Change-Id: I016ba718d2dd27ec25b8590d1563116753e89437