minijail0: use exit(0) with -H help

This isn't an error path, so exit(0) when the user requested this output.

Bug: None
Test: `./minijail -H; echo $?` shows 0 now
Change-Id: I144b7980d1d85f9d408788bbe42544d431a1aa42
diff --git a/minijail0.c b/minijail0.c
index 425fbf0..a434953 100644
--- a/minijail0.c
+++ b/minijail0.c
@@ -567,7 +567,7 @@
 			break;
 		case 'H':
 			seccomp_filter_usage(argv[0]);
-			exit(1);
+			exit(0);
 		case 'I':
 			minijail_namespace_pids(j);
 			minijail_run_as_init(j);