Add const specifiers to pacify armclang

Functions designed for local scope only should be const

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/tests/src/bignum_codepath_check.c b/tests/src/bignum_codepath_check.c
index b752d13..9c6bbc7 100644
--- a/tests/src/bignum_codepath_check.c
+++ b/tests/src/bignum_codepath_check.c
@@ -11,14 +11,14 @@
 #if defined(MBEDTLS_TEST_HOOKS) && !defined(MBEDTLS_THREADING_C)
 int mbedtls_codepath_check = MBEDTLS_MPI_IS_TEST;
 
-void mbedtls_codepath_take_safe(void)
+static void mbedtls_codepath_take_safe(void)
 {
     if (mbedtls_codepath_check == MBEDTLS_MPI_IS_TEST) {
         mbedtls_codepath_check = MBEDTLS_MPI_IS_SECRET;
     }
 }
 
-void mbedtls_codepath_take_unsafe(void)
+static void mbedtls_codepath_take_unsafe(void)
 {
     mbedtls_codepath_check = MBEDTLS_MPI_IS_PUBLIC;
 }