Merge #232

232: update tock submodule to fix CI r=jrvanwhy a=hudson-ayers

This updates the Tock submodule to current master to bring in this fix: https://github.com/tock/tock/commit/b58812b63f1682d008ceab881121b27a301f3af8 which updated the OpenTitan boot ROM download location.

Co-authored-by: Hudson Ayers <hayers@stanford.edu>