eap-sim-file: Fix build with DEBUG_LEVEL < 1

src/libcharon/plugins/eap_sim_file/eap_sim_file_triplets.c

@@ -157,7 +157,7 @@ static bool read_triplets(private_eap_sim_file_triplets_t *this, char *path)
 {
 	char line[512];
 	FILE *file;
-	int i, nr = 0;
+	int i, nr DBG_UNUSED = 0;
 
 	file = fopen(path, "r");
 	if (file == NULL)