include: Fix a typo

[Andrew Talbot]

Changelog:
    include: Fix a typo.

diff --git a/include/guiddef.h b/include/guiddef.h
index ba8e8cf..b70175e 100644
--- a/include/guiddef.h
+++ b/include/guiddef.h
@@ -83,7 +83,7 @@ extern "C++" {
 #define _GUIDDEF_H_
 
 #ifndef __LPGUID_DEFINED__
-#define __LPGUID_DEFINED___
+#define __LPGUID_DEFINED__
 typedef GUID *LPGUID;
 #endif