[InstCombine] Fix incorrect fshr to fshl transform

This transform is only valid if the (modular) shift amount is not
zero.

Proof: https://alive2.llvm.org/ce/z/WBxn-x

Fixes https://github.com/llvm/llvm-project/issues/89338.

GitOrigin-RevId: 46957a138dea339799059ea5bf032e40042ff185
2 files changed