Add missing include

Signed-off-by: Werner Lewis <werner.lewis@arm.com>
diff --git a/tests/suites/test_suite_bignum_mod_raw.function b/tests/suites/test_suite_bignum_mod_raw.function
index 099c944..18ac97f 100644
--- a/tests/suites/test_suite_bignum_mod_raw.function
+++ b/tests/suites/test_suite_bignum_mod_raw.function
@@ -1,6 +1,7 @@
 /* BEGIN_HEADER */
 #include "mbedtls/bignum.h"
 #include "mbedtls/entropy.h"
+#include "bignum_core.h"
 #include "bignum_mod_raw.h"
 #include "constant_time_internal.h"
 #include "test/constant_flow.h"