[Clang][NFCI] Fix a logic issue in TransformDesignatedInitExpr (#127211)

It was clearly a typo regarding whether the array index expression has changed in its transforming.

This doesn't appear to be a functional change in practice, so no test case or release note provided.

Fixes #126113

Author: GS-GOAT

clang/lib/Sema/TreeTransform.h

@@ -13672,7 +13672,7 @@ TreeTransform<Derived>::TransformDesignatedInitExpr(DesignatedInitExpr *E) {
       Desig.AddDesignator(
           Designator::CreateArrayDesignator(Index.get(), D.getLBracketLoc()));
 
-      ExprChanged = ExprChanged || Init.get() != E->getArrayIndex(D);
+      ExprChanged = ExprChanged || Index.get() != E->getArrayIndex(D);
       ArrayExprs.push_back(Index.get());
       continue;
     }