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>