vtls.h: Fixed compiler warning when compiled without SSL

vtls.c:185:46: warning: unused parameter 'data'

lib/vtls/vtls.h

@@ -134,7 +134,7 @@ CURLcode Curl_pin_peer_pubkey(const char *pinnedpubkey,
 #define Curl_ssl_free_certinfo(x) Curl_nop_stmt
 #define Curl_ssl_connect_nonblocking(x,y,z) CURLE_NOT_BUILT_IN
 #define Curl_ssl_kill_session(x) Curl_nop_stmt
-#define Curl_ssl_random(x,y,z) CURLE_NOT_BUILT_IN
+#define Curl_ssl_random(x,y,z) ((void)x, CURLE_NOT_BUILT_IN)
 #define CURL_SSL_BACKEND CURLSSLBACKEND_NONE
 #endif