Clear target allocation as is_initial flag as true

In the multple CISes phone call case, the is_initial flag will be cleaned after the stack update the target allocation to the bluetooth audio HAL, but the stack will build the target allocation multple times, it would be the target allocation stream map will contain the duplicated data, need to clear the stream_map as is_initial flag still be true.

Bug: 248063359
Fixes: 248063359
Test: atest atest bluetooth_le_audio_test
Test: LE audio phone call on offload path
Change-Id: Icc74c3fc787a2227b331a028efd72f9bd2ef2721
Merged-In: Icc74c3fc787a2227b331a028efd72f9bd2ef2721
(cherry picked from commit 65a48f15)