test(slot buffer): add assertion tests

This patch also fixes the dest and src addresses not being checked for
ns_buffer_read() and ns_buffer_write() respectively as well as some
lines exceeding 80 cols on granule.cpp

Signed-off-by: Javier Almansa Sobrino <javier.almansasobrino@arm.com>
Change-Id: I71cac6e85294fac828c950b227cf9d9fb27164ae
diff --git a/lib/realm/src/buffer.c b/lib/realm/src/buffer.c
index 687d86f..e7e69b6 100644
--- a/lib/realm/src/buffer.c
+++ b/lib/realm/src/buffer.c
@@ -282,6 +282,7 @@
 
 	assert(is_ns_slot(slot));
 	assert(ns_gr != NULL);
+	assert(dest != NULL);
 
 	/*
 	 * To simplify the trapping mechanism around NS access,
@@ -321,6 +322,7 @@
 
 	assert(is_ns_slot(slot));
 	assert(ns_gr != NULL);
+	assert(src != NULL);
 
 	/*
 	 * To simplify the trapping mechanism around NS access,