[XLA:CPU] Make EmitTargetAddressForOp return void (well, technically Status).

This is a general cleanup -- less repeated code -- but it's also part of
an effort to use IrArray more and llvm::Value less.  In particular, many
callsites would take the llvm::Value returned by EmitTargetAddressForOp
and create an IrArray out of it, but then never attach AA info to that
array.  Having this function return void forces you to call
GetIrArrayForOp(), which attaches the AA metadata appropriately.

This change also gets rid of an unused arg to EmitTargetAddressForOp.

PiperOrigin-RevId: 171320201