Change GetProcAddr  function signature to use XGL types.

Fix bug in GPA for basic_plugin.c .
diff --git a/xgl.py b/xgl.py
index dbdd063..857eea7 100644
--- a/xgl.py
+++ b/xgl.py
@@ -87,7 +87,7 @@
 
 # XGL core API
 core = (
-    Proto("void *", "GetProcAddr",
+    Proto("XGL_VOID *", "GetProcAddr",
         (Param("XGL_PHYSICAL_GPU", "gpu"),
          Param("const XGL_CHAR*", "pName"))),