fix a couple of compilation errors.

common.h

@@ -471,7 +471,9 @@ void mutex_unlock(void *arg);
 void mutex_cleanup(void *arg);
 void cv_cleanup(void *arg);
 void thread_cleanup(void *arg);
+#ifdef CONFIG_AIRPLAY_2
 void plist_cleanup(void *arg);
+#endif
 
 char *debug_malloc_hex_cstring(void *packet, size_t nread);