Decompile GetLinkState arm9 function

This is not part of the `LinkStateItem` class, but it is called by
a method in that class. I wasn't sure the best place to put this.

src/Main/Player/LinkState.cpp

@@ -0,0 +1,5 @@
+#include "Player/LinkStateBase.hpp"
+
+unk32 GetLinkState(s32 index) {
+    return (unk32)gLinkStates[index];
+}