[llvm] [AMDGPU] Fix GCNUpwardRPTracker: max register pressure on defs. (PR #74422)

[Valery Pykhtin via llvm-commits]

vpykhtin wrote:

> The idea here is that all defs (whether they are early-clobber or not) are simultaneously live "at" the instruction, right? Hopefully that matches how the register allocator handles them.

right, thank you Jay!

https://github.com/llvm/llvm-project/pull/74422