m/n/c/localstorage: fix synchronous mounting flag

As it turns out, MS_SYNC is not actually a mount(2) flag anymore,
only MS_SYNCHRONOUS is.

Change-Id: I4d2adbdf1a335b35a6c1e5d3725ee5451f6b5339
Reviewed-on: https://review.monogon.dev/c/monogon/+/671
Reviewed-by: Sergiusz Bazanski <serge@monogon.tech>
diff --git a/metropolis/node/core/localstorage/directory_root.go b/metropolis/node/core/localstorage/directory_root.go
index c3a49cb..44af268 100644
--- a/metropolis/node/core/localstorage/directory_root.go
+++ b/metropolis/node/core/localstorage/directory_root.go
@@ -39,7 +39,7 @@
 		return fmt.Errorf("MakeBlockDevices: %w", err)
 	}
 
-	if err := unix.Mount(crypt.ESPDevicePath, r.ESP.FullPath(), "vfat", unix.MS_NOEXEC|unix.MS_NODEV|unix.MS_SYNC, ""); err != nil {
+	if err := unix.Mount(crypt.ESPDevicePath, r.ESP.FullPath(), "vfat", unix.MS_NOEXEC|unix.MS_NODEV|unix.MS_SYNCHRONOUS, ""); err != nil {
 		return fmt.Errorf("mounting ESP partition: %w", err)
 	}