[mlir] Fix -Wrange-loo-analysis warnings

for (const auto &x : llvm::zip(..., ...))

->

for (auto x : llvm::zip(..., ...))

The return type of zip() is a wrapper that wraps a tuple of references.

> warning: loop variable 'p' is always a copy because the range of type 'detail::zippy<detail::zip_shortest, ArrayRef<long> &, ArrayRef<long> &>' does not return a reference [-Wrange-loop-analysis]