[NFC][x86] Cleanup X86FrameLowering::emitSPUpdate (#156948)

I was trying to understand the cases where `emitSPUpdate` may use a
`push` to adjust the stack pointer and realized that the code was more
complex than it needed to be.

* `Chunk` is redundant as it is set to `MaxSPChunk` and never modified.
* The only time we use the `push` optimization is if `Offset` is equal
to `SlotSize` (as `SlotSize` is never as large as `MaxSPChunk`, so will
never equal if `std::min` returned that value).
* If we use the `push` optimization, then we've finished adjusting the
stack and can return early instead of continuing the loop.

0 files changed, 0 insertions, 0 deletions