[clang] [mlir][llvm] Fix elem type passing into `getelementptr` (PR #68136)

[Markus Böck via cfe-commits]

zero9178 wrote:

What are the use cases for allowing either of these two syntaxes?
The LLVM Dialect tries to closely mirror LLVM proper as much as possible and this would deviate from LLVMs behaviour. While the transition is currently stalled, in the future typed pointers will be removed from the dialect entirely, further discouraging the use of typed-pointers such as shown here.

https://github.com/llvm/llvm-project/pull/68136