Change write_sig_alg_ext of tls12

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index d6b3baa..8cdeb8d 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -6858,14 +6858,18 @@
 int mbedtls_ssl_check_sig_hash( const mbedtls_ssl_context *ssl,
                                 mbedtls_md_type_t md )
 {
-    const int *cur = mbedtls_ssl_conf_get_sig_algs( ssl->conf );
 
-    if( cur == NULL )
+    const uint16_t *sig_alg = mbedtls_ssl_conf_get_sig_algs( ssl->conf );
+    if( sig_alg == NULL )
         return( -1 );
 
-    for( ; *cur != MBEDTLS_MD_NONE; cur++ )
-        if( *cur == (int) md )
+    for( ; *sig_alg != MBEDTLS_TLS1_3_SIG_NONE; sig_alg++ )
+    {
+        mbedtls_md_type_t hash = mbedtls_ssl_md_alg_from_hash(
+                                                    ( *sig_alg >> 8 ) & 0xff );
+        if( hash == md )
             return( 0 );
+    }
 
     return( -1 );
 }