Replace directly access for sig_hashes

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index a137e43..9eaeab4 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -2798,7 +2798,8 @@
         /*
          * Supported signature algorithms
          */
-        for( cur = ssl->conf->sig_hashes; *cur != MBEDTLS_MD_NONE; cur++ )
+        for( cur = mbedtls_ssl_conf_get_sig_algs( ssl->conf );
+             *cur != MBEDTLS_MD_NONE; cur++ )
         {
             unsigned char hash = mbedtls_ssl_hash_from_md_alg( *cur );