[llvm] [AMDGPU] Fix computeKnownBitsForTargetNode for AMDGPUISD::LDS (PR #210350)

[Jay Foad via llvm-commits]

jayfoad wrote:

> LGTM except the changed test looks random and incidental?

It is (incidentally) testing whether the alignment of this GV implies that its address is zero, which is true if you have no more than 64 KiB of LDS:
```
@esgs_ring = external addrspace(3) global [0 x i32], align 65536
```
I don't know how to write a more targeted test for this.

https://github.com/llvm/llvm-project/pull/210350