sink: guard against zero frame size in free-frames

Free-frames divided the free size by the frame size, which is channels
times sample size and can be zero when the channel count is zero. Return
zero instead of dividing by zero.

Signed-off-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>

Author: lrgirdwo

src/module/audio/sink_api.c

@@ -109,7 +109,15 @@ EXPORT_SYMBOL(sink_get_frame_bytes);
 
 size_t sink_get_free_frames(struct sof_sink *sink)
 {
-	return sink_get_free_size(sink) / sink_get_frame_bytes(sink);
+	size_t frame_bytes = sink_get_frame_bytes(sink);
+
+	/* frame_bytes is channels * sample_size and both are host-influenced;
+	 * guard against a zero divisor (e.g. channels == 0)
+	 */
+	if (!frame_bytes)
+		return 0;
+
+	return sink_get_free_size(sink) / frame_bytes;
 }
 EXPORT_SYMBOL(sink_get_free_frames);