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.

include/Player/LinkStateBase.hpp

@@ -128,3 +128,7 @@ public:
     DebugHierarchy *GetDebugHierarchy0();
     DebugHierarchy *GetDebugHierarchy1();
 };
+
+unk32 GetLinkState(s32 index);
+
+extern LinkStateBase **gLinkStates;