Set filename in ZSM backend

backends/playback/zsm/zsm_backend.cpp

@@ -39,6 +39,7 @@ std::vector<Property> ZsmBackend::get_property_list() {
 }
 void ZsmBackend::load(const char *filename) {
 	memset(&spec, 0, sizeof(spec));
+    current_file = filename;
     spec.format = AUDIO_S16SYS;
     spec.samples = 100;
     spec.channels = 2;