[owners] Update OWNERs file to libpng

Change-Id: I1c36a7b39e240f24a264dfd2d862fffdbc3fc696
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/libpng/+/557962
Reviewed-by: David Reveman <reveman@google.com>
1 file changed