fix(rss): fix build issues with comms protocol

Signed-off-by: Tamas Ban <tamas.ban@arm.com>
Change-Id: I77d2d3c5ac39a840b768f84f859d76b3965749aa
diff --git a/drivers/arm/rss/rss_comms_protocol.c b/drivers/arm/rss/rss_comms_protocol.c
index 4b3de54..a8d1dda 100644
--- a/drivers/arm/rss/rss_comms_protocol.c
+++ b/drivers/arm/rss/rss_comms_protocol.c
@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-3-Clause
  *
  */
+#include <assert.h>
 
 #include <common/debug.h>
 #include "rss_comms_protocol.h"