[llvm] [TableGen] Fix minor index bugs in PseudoLoweringEmitter (PR #81605)

[Alfie Richards via llvm-commits]

AlfieRichardsArm wrote:

Hi @s-barannikov,

Apologies, I have moved to working in GCC so haven’t kept up with this patch. 

I think this patch can be closed. These bugs likely still exist, but only came up when I was trying to make .n and .w optional operands, which is indefinitely paused. 

https://github.com/llvm/llvm-project/pull/81605