[llvm] [EarlyIfConversion] Fix the logic to determine predictable branch. (PR #92405)

[Mikhail Gudim via llvm-commits]

mgudim wrote:

@fhahn @sjoerdmeijer Shouldn't calling `MachineLoop::isLoopInvariant` on the branch instruction be enough (ideally)?

https://github.com/llvm/llvm-project/pull/92405