Shape functions: Use friendlier clamping pattern
When start_val == 0, using the comparison `start_val > self[dim]` can be folded easily (0 is never strictly greater than the result of `self[dim]`), but `start_val >= self[dim]` can't. Since we assign `start_val = sef[dim]` in the body anyway, both these are equivalent
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74980
Approved by: https://github.com/eellison
