greybus: add copyright statements

The Greybus audio source files included no copyright statements.
Add them.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
diff --git a/drivers/staging/greybus/audio-dai.c b/drivers/staging/greybus/audio-dai.c
index 0dd7364..9b162bf 100644
--- a/drivers/staging/greybus/audio-dai.c
+++ b/drivers/staging/greybus/audio-dai.c
@@ -1,3 +1,12 @@
+/*
+ * Greybus audio Digital Audio Interface (DAI) driver
+ *
+ * Copyright 2015 Google Inc.
+ * Copyright 2015 Linaro Ltd.
+ *
+ * Released under the GPLv2 only.
+ */
+
 #include <linux/kernel.h>
 #include <linux/device.h>
 #include <linux/interrupt.h>