[llvm] [SPARC] Fix regression from UpgradeDataLayoutString change (PR #110608)

[via llvm-commits]

koachan wrote:

> Wouldn't it be enough to drop the assertion?
> 
> If the datalayout is already "incorrect" to the point that it does not have i64 alignment, it probably doesn't make sense to add i128 alignment?

Hmm, yeah, turning the assert into an if seem to work too. I guess it's better like this.

https://github.com/llvm/llvm-project/pull/110608