[llvm] [llvm][NFC] Use SDValue::getConstantOperandVal(i) where possible (PR #76708)

[Alex Bradbury via llvm-commits]

asb wrote:

The getConstantOperandAPInt equivalent to this was committed directly in a181b425659a. Far fewer opportunities (though there are some more if we add a `SDNode::getAsAPIntVal()` helper).

https://github.com/llvm/llvm-project/pull/76708