greybus: fix a bug in gb_operation_gbuf_complete()

The gbuf completion routine was using the request payload pointers
(which point at the area *past* the message header) rather than the
header.  This didn't matter much for now, it was only used in the
error path.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/staging/greybus/operation.c

@@ -283,9 +283,9 @@ static void gb_operation_gbuf_complete(struct gbuf *gbuf)
 		int type;
 
 		if (gbuf == operation->request)
-			header = operation->request_payload;
+			header = operation->request->transfer_buffer;
 		else if (gbuf == operation->response)
-			header = operation->response_payload;
+			header = operation->response->transfer_buffer;
 		else
 			header = NULL;