graphics/oidn: Replace format=bsdtar with format=ustar
... because the undocumented format bsdtar adds paxheaders on
some systems, therefore breaking the fetch.
The documentation for format=bsdtar should be added:
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=277139
PR: 253814
Reported by: Mamoru IWAKI <1wkmmr@gmail.com>
(cherry picked from commit c22e29d08774bc5ad5eee4406ae59898c5903619)