Return zero_point from determine_qparams as a int64 (#98746)
Summary:
In some cases, zero_point is returned as an int tensor. We want it to be a long.
This fixes a failed assertion in Executorch op_choose_qparams:
https://www.internalfb.com/code/fbsource/[4609e7dbbf2e]/fbcode/executorch/kernels/quantized/cpu/op_choose_qparams.cpp?lines=49-52
Test Plan: CI
Reviewed By: jerryzh168
Differential Revision: D44764070
Pull Request resolved: https://github.com/pytorch/pytorch/pull/98746
Approved by: https://github.com/jerryzh168
