fix clang build fail

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_tls13_keys.c b/library/ssl_tls13_keys.c
index ea0c55b..88f0fe5 100644
--- a/library/ssl_tls13_keys.c
+++ b/library/ssl_tls13_keys.c
@@ -655,7 +655,6 @@
     size_t transcript_len;
 
     unsigned char *base_key = NULL;
-    size_t base_key_len;
 
     mbedtls_md_type_t const md_type = ssl->handshake->ciphersuite_info->mac;
     const mbedtls_md_info_t* const md_info =
@@ -678,15 +677,9 @@
     MBEDTLS_SSL_DEBUG_BUF( 4, "handshake hash", transcript, transcript_len );
 
     if( from == MBEDTLS_SSL_IS_CLIENT )
-    {
         base_key = ssl->handshake->tls13_hs_secrets.client_handshake_traffic_secret;
-        base_key_len = sizeof( ssl->handshake->tls13_hs_secrets.client_handshake_traffic_secret );
-    }
     else
-    {
         base_key = ssl->handshake->tls13_hs_secrets.server_handshake_traffic_secret;
-        base_key_len = sizeof( ssl->handshake->tls13_hs_secrets.server_handshake_traffic_secret );
-    }
 
     ret = ssl_tls13_calc_finished_core( md_type, base_key, transcript, dst );
     if( ret != 0 )
@@ -698,7 +691,10 @@
 
 exit:
     /* Erase handshake secrets */
-    mbedtls_platform_zeroize( base_key, base_key_len );
+    if( from == MBEDTLS_SSL_IS_CLIENT )
+        mbedtls_platform_zeroize( base_key, sizeof( ssl->handshake->tls13_hs_secrets.client_handshake_traffic_secret ) );
+    else
+        mbedtls_platform_zeroize( base_key, sizeof( ssl->handshake->tls13_hs_secrets.server_handshake_traffic_secret ) );
     mbedtls_platform_zeroize( transcript, sizeof( transcript ) );
     return( ret );
 }