leaudio: Fix attaching late device to the stream

Make sure, the stream state and target state are STREAMING before
attaching device to the stream.
By checking TargetState we are making sure that stream is no in
transition to Idle.

Bug: 287260361
Test: atest  BluetoothInstrumentationTest
Test: manual
Tag: #feature
Change-Id: I53615d194c20cccb183105d9896498a5d0f32b8a