audio: stub get_next_write_timestamp() function

get_next_write_timestamp() is not used by FUGU and
should return an error and be a NO OP.

Bug: 22658402.
Change-Id: I554cff099eb003279a1f0b505d6cc737c55c3aaa
diff --git a/libaudio/audio_hal_thunks.cpp b/libaudio/audio_hal_thunks.cpp
index 1550d04..4c0ec40 100644
--- a/libaudio/audio_hal_thunks.cpp
+++ b/libaudio/audio_hal_thunks.cpp
@@ -207,13 +207,10 @@
     return tstream->impl->getPresentationPosition(frames, timestamp);
 }
 
-static int out_get_next_write_timestamp(const struct audio_stream_out *stream,
-                                        int64_t *timestamp)
+static int out_get_next_write_timestamp(const struct audio_stream_out *stream __unused,
+                                        int64_t *timestamp __unused)
 {
-    const struct atv_stream_out* tstream =
-        reinterpret_cast<const struct atv_stream_out*>(stream);
-
-    return tstream->impl->getNextWriteTimestamp(timestamp);
+    return -ENOSYS;
 }
 
 static int out_pause(struct audio_stream_out* stream)