HID: lenovo: Sync Fn-lock state on button press for Compact and TrackPoint II keyboards

When Fn-Esc is pressed on the keyboard, it emits the scancode which could
be used to sync the fn_lock sysfs state.

Previously fn_lock only allowed to set new Fn-lock state and did not
keep the value in sync upon Fn-Esc press, which is now fixed.
Signed-off-by: Florian Klink <flokli@flokli.de>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-lenovo.c

@@ -690,6 +690,15 @@ static int lenovo_event_cptkbd(struct hid_device *hdev,
 		return 1;
 	}
 
+	if (usage->type == EV_KEY && usage->code == KEY_FN_ESC && value == 1) {
+		/*
+		 * The user has toggled the Fn-lock state. Toggle our own
+		 * cached value of it and sync our value to the keyboard to
+		 * ensure things are in sync (the syncing should be a no-op).
+		 */
+		cptkbd_data->fn_lock = !cptkbd_data->fn_lock;
+	}
+
 	return 0;
 }