audio: fix capture problem

Reset input buffer frame count when starting capture to
avoid reading stale data from previous capture.

Change-Id: Ied07eda9b2094b8a36f07871d6e071ac96f5892d
diff --git a/audio/audio_hw.c b/audio/audio_hw.c
index 72f1359..3182c00 100644
--- a/audio/audio_hw.c
+++ b/audio/audio_hw.c
@@ -383,6 +383,7 @@
     in->buffer_size = pcm_frames_to_bytes(in->pcm,
                                           in->pcm_config->period_size);
     in->buffer = malloc(in->buffer_size);
+    in->frames_in = 0;
 
     adev->active_in = in;