[llvm] [llvm][CodeGen] Fixed a bug in stall cycle calculation for window scheduler (PR #99451)

[Hua Tian via llvm-commits]

huaatian wrote:

> Does this affect codegen correctness or is this just resulting in suboptimal codegen? If it is the former, should this be backported to 19.x?

This is just resulting in suboptimal codegen.  Since all stall cycles increase by 1, there is relatively no change.

https://github.com/llvm/llvm-project/pull/99451