better messages

lib/fimg-core.c

@@ -158,7 +158,7 @@ fprintf(stderr, ">>> %-25s ( %p )\n", __func__, fimg);
 #endif
 
 if (NULL == fimg) {
-	fprintf(stderr, "%s : parameter is null\n", __func__);
+	fprintf(stderr, "%s : descriptor address is null\n", __func__);
 	return -1;
 	}