Test: Increase stack size of SST NS test threads

Increases the stack size to prevent running out of stack in some
configs.

Change-Id: I524da6d5b41ed1ca056ec9fbacc4f4509bf7702e
Signed-off-by: Jamie Fox <jamie.fox@arm.com>
diff --git a/test/suites/sst/non_secure/ns_test_helpers.c b/test/suites/sst/non_secure/ns_test_helpers.c
index e1f8f7e..9dc18bc 100644
--- a/test/suites/sst/non_secure/ns_test_helpers.c
+++ b/test/suites/sst/non_secure/ns_test_helpers.c
@@ -11,7 +11,7 @@
 
 #include "tfm_nspm_api.h"
 
-#define SST_TEST_TASK_STACK_SIZE (512)
+#define SST_TEST_TASK_STACK_SIZE (768)
 
 struct test_task_t {
     test_func_t *func;