cmGlobalVisualStudio7Generator: fix initialization typo

Typo introduced in b82a74d918 (generators: use GetSupportDirectory() in
more places, 2025-05-21) via !10812. Pointed out in a PVS-Studio blog
post.

See: https://pvs-studio.com/en/blog/posts/cpp/1277/ (N3)

Source/cmGlobalVisualStudio7Generator.cxx

@@ -623,7 +623,7 @@ std::string cmGlobalVisualStudio7Generator::WriteUtilityDepend(
     target->GetLocalGenerator()->MaybeRelativeToCurBinDir(
       cmStrCat(target->GetSupportDirectory(), '\\'));
   for (std::string const& i : configs) {
-    std::string intDir = cmStrCat(intDir, i);
+    std::string intDir = cmStrCat(intDirPrefix, i);
 
     /* clang-format off */
     fout <<