userspace: mark arguments used

Reviewed-by: Alejandro Colomar <alx.manpages@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13110

contrib/pam_zfs_key/pam_zfs_key.c

@@ -47,6 +47,7 @@
 static void
 pam_syslog(pam_handle_t *pamh, int loglevel, const char *fmt, ...)
 {
+	(void) pamh;
 	va_list args;
 	va_start(args, fmt);
 	vsyslog(loglevel, fmt, args);