audio: Implement get_capture_position()

Change-Id: Ib9f637d30774b2a9aa23e6958ce5465d90eae467
diff --git a/audio/audio_hw.h b/audio/audio_hw.h
index 6e58a11..d2c6e0f 100644
--- a/audio/audio_hw.h
+++ b/audio/audio_hw.h
@@ -363,6 +363,8 @@
     bool                                is_fastcapture_affinity_set;
 
     int64_t                             last_read_time_us;
+    int64_t                             frames_read; /* total frames read, not cleared when
+                                                        entering standby */
 };
 
 struct mixer_card {