[llvm] AMDGPU/GlobalISel: Fix tablegen definition for G_AMDGPU_LOAD_D16 (PR #158039)

[Petar Avramovic via llvm-commits]

petar-avramovic wrote:

### Merge activity

* **Sep 11, 11:39 AM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/158039).


https://github.com/llvm/llvm-project/pull/158039