ntdll: Fix runtime availability check for pthread_attr_set_qos_class_np.

dlls/ntdll/unix/loader.c

@@ -2336,7 +2336,7 @@ static void apple_create_wine_thread( void *arg )
     pthread_attr_init( &attr );
     pthread_attr_setdetachstate( &attr, PTHREAD_CREATE_JOINABLE );
     /* Use the same QoS class as the process main thread (user-interactive). */
-    if (pthread_attr_set_qos_class_np)
+    if (&pthread_attr_set_qos_class_np)
         pthread_attr_set_qos_class_np( &attr, QOS_CLASS_USER_INTERACTIVE, 0 );
     if (pthread_create( &thread, &attr, apple_wine_thread, NULL )) exit(1);
     pthread_attr_destroy( &attr );