Fixes false walls icons using the wrong icon files (#80175)

## About The Pull Request

Closes #80180

I was trying to merge https://github.com/tgstation/tgstation/pull/79659/
downstream and I couldn't figure out why the false wall icons were not
showing up ingame--turns out there was a bug.

The icon files for false walls and the 'fake' (normal wall) version were
just in each others' spots and needed to be swapped.

## Why It's Good For The Game

<details><summary>No more invisible sprites</summary>


![dreamseeker_4JbR2TXVK5](https://github.com/tgstation/tgstation/assets/13398309/10d1ed47-2806-4051-bff7-0bd63e132bc0)

</details>

## Changelog

🆑
fix: false walls icons will now display again
/🆑

code/game/objects/structures/false_walls.dm

@@ -73,14 +73,14 @@
 
 /obj/structure/falsewall/update_icon_state()
 	if(opening)
-		icon = fake_icon
+		icon = initial(icon)
 		icon_state = "[base_icon_state]-[density ? "opening" : "closing"]"
 		return ..()
 	if(density)
-		icon = initial(icon)
+		icon = fake_icon
 		icon_state = "[base_icon_state]-[smoothing_junction]"
 	else
-		icon = fake_icon
+		icon = initial(icon)
 		icon_state = "[base_icon_state]-open"
 	return ..()