[mlir][NFC] Fix compilation error downstream when `NDEBUG` is defined

If the LLVM build used was compiled with `LLVM_ENABLE_ABI_BREAKING_CHECKS` but the header was included with `NDEBUG` defined, a compilation error would occur as there is a pack expansion operator (`...`), but no variadic arguments existed. This was due to the assert being preprocessed to an empty expression.

This commit moves the pack expansion within the `assert` to also be removed with the `assert`.