Fix iOS CHIPTool build. (#6514)

This is due to a merge conflict between PR #6233 nd PR #6442.  The
completion handlers got renamed to response handlers in the latter,
but the former is still calling one of them completionHandler.

src/darwin/CHIPTool/CHIPTool/View Controllers/QRCode/QRCodeViewController.m

@@ -374,7 +374,7 @@ - (void)setVendorIDOnAccessory
                                                                                          endpoint:0
                                                                                             queue:dispatch_get_main_queue()];
         [opCreds setFabric:kCHIPToolTmpVendorId
-            completionHandler:^(NSError * _Nullable error, NSDictionary * _Nullable values) {
+            responseHandler:^(NSError * _Nullable error, NSDictionary * _Nullable values) {
                 if (error.code != CHIPSuccess) {
                     NSLog(@"Got back error trying to getFabricId %@", error);
                 } else {