prevent compiler warning

lib/ssluse.c

@@ -1050,7 +1050,7 @@ static void ssl_tls_trace(int direction, int ssl_ver, int content_type,
   Curl_debug(data, CURLINFO_TEXT, ssl_buf, txt_len, NULL);
 
   Curl_debug(data, (direction == 1) ? CURLINFO_SSL_DATA_OUT :
-             CURLINFO_SSL_DATA_IN, buf, len, NULL);
+             CURLINFO_SSL_DATA_IN, (char *)buf, len, NULL);
   (void) ssl;
 }
 #endif