[Inductor] Fix a dynamic shape problem when lowering diagonal (#121881)
Summary: when computing the diagonal size, we need to use correct symbolic min/max function.
Differential Revision: [D54884899](https://our.internmc.facebook.com/intern/diff/D54884899)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121881
Approved by: https://github.com/aakhundov
