[AArch64][X86] xor.ll - fix vec_add_of_not_with_undef_decrement copy+pasta typo

This was copied from vec_add_of_not_with_undef instead of vec_add_of_not_decrement - replacing the second sub with an add

GitOrigin-RevId: 7fbdadb68e259079d23165ecb94e2893a3823576
2 files changed