hal: Avoid stereo device selection for target with single speaker

Stereo flag is true by default, speaker device in selection
of VOICE_SPEAKER_2 during call for target with single speaker.
Fix this by set stereo flag to false for target with single
speaker to ensure proper speaker device is selected.

Change-Id: I4733270abbbce1fba976e191abef84e0710bdfca
1 file changed