leaudio: Remove duplicate logic

In the beginning of `GetAudioSessionCodecConfigForDirection()`, the
logic is same as GetConfiguration(). Change to use Getconfiguration() to
remove duplicate code.

Bug: 259191520
Flag: Exempt, no functional change. Regression tested with unittests
Test: atest bluetooth_le_audio_test bluetooth_le_audio_client_test
Change-Id: If733d4acf00135f39b2b44013752875e2e3934b4