Fix cleanups crashes in `vla.c`

[bcardosolopes]

BTW, I ran into an issue with vla.c yesterday related with cleanups when adding more skeletons to complete function epilogue, see the FIXME's in https://github.com/llvm/clangir/commit/eaf965e20f62e81586d4862d3697ac4720e19468. This is hinting to the possibility that such cleanups could be slightly wrong, or there's something missing in this PR.

Originally posted by @bcardosolopes in https://github.com/llvm/clangir/issues/453#issuecomment-1936678297