[v4] iommu/riscv: prevent NULL deref in iova_to_phys

[XianLiang Huang]

> Does it trigger undesirable communication difficulties?
No, and I agree that both subject and summary phrase can be improved

And now I do learn from this, thanks.
> Your patch will almost certainly get comments from reviewers on ways in
> which the patch can be improved, in the form of a reply to your email. You must
> respond to those comments; ignoring reviewers is a good way to get ignored in
> return. You can simply reply to their emails to answer their comments. Review
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst#n310

Regards,
Xianliang