Fix compilation with /Zc:strictStrings

You can't assign a wide-character literal to a non-const wchar_t*.

Change-Id: I3ec8d4064f8e901bb1c6ff14cdf41550b04c593d
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>

src/plugins/platforms/windows/accessible/iaccessible2.h

@@ -329,7 +329,7 @@ public:
 private:
     static BSTR relationToBSTR(QAccessible::Relation relation)
     {
-        wchar_t *constRelationString = 0;
+        const wchar_t *constRelationString = 0;
         switch (relation) {
         case QAccessible::Label:
             constRelationString = IA2_RELATION_LABEL_FOR;