dmfilemapd: return error for wrong number of args

The initial check on argc incorrectly returns 1 when the wrong
number of arguments are present, causing a segfault in main()
when no arguments are given:

  # dmfilemapd
  Wrong number of arguments.
  usage: dmfilemapd <fd> <group_id> <path> <mode> [<foreground>[<log_level>]]
  Segmentation fault (core dumped)

daemons/dmfilemapd/dmfilemapd.c

@@ -255,7 +255,7 @@ static int _parse_args(int argc, char **argv, struct filemap_monitor *fm)
 	if (argc < 5) {
 		_early_log("Wrong number of arguments.");
 		_early_log("usage: %s", _usage);
-		return 1;
+		return 0;
 	}
 
 	memset(fm, 0, sizeof(*fm));