[llvm] AMDGPU/GlobalISel: Report RegBankLegalize errors using reportGISelFailure (PR #169918)

[Petar Avramovic via llvm-commits]

petar-avramovic wrote:

### Merge activity

* **Dec 2, 10:47 PM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.com/github/pr/llvm/llvm-project/169918).


https://github.com/llvm/llvm-project/pull/169918