selftests/landlock: Fix a resource leak

The opened file should be closed before return, otherwise resource leak
will occur.

Signed-off-by: Ding Xiang <dingxiang@cmss.chinamobile.com>
Link: https://lore.kernel.org/r/20230830101148.3738-1-dingxiang@cmss.chinamobile.com
Fixes: 3de64b6 ("selftests/landlock: Add supports_filesystem() helper")
Signed-off-by: Mickaël Salaün <mic@digikod.net>

Author: Ding Xiang

tools/testing/selftests/landlock/fs_test.c

@@ -113,7 +113,7 @@ static bool supports_filesystem(const char *const filesystem)
 {
 	char str[32];
 	int len;
-	bool res;
+	bool res = true;
 	FILE *const inf = fopen("/proc/filesystems", "r");
 
 	/*
@@ -125,14 +125,16 @@ static bool supports_filesystem(const char *const filesystem)
 
 	/* filesystem can be null for bind mounts. */
 	if (!filesystem)
-		return true;
+		goto out;
 
 	len = snprintf(str, sizeof(str), "nodev\t%s\n", filesystem);
 	if (len >= sizeof(str))
 		/* Ignores too-long filesystem names. */
-		return true;
+		goto out;
 
 	res = fgrep(inf, str);
+
+out:
 	fclose(inf);
 	return res;
 }