getentropy: Add Git hashes corresponding to SVN references

getentropy has a comment about a special case to support kernels between
SVN revisions r331280 and r337999. Add the corresponding Git hashes so
there's a usable reference after Subversion infrastructure disappears.

Sponsored by: The FreeBSD Foundation

(cherry picked from commit 4ef07eb0802a6353faf79d58719d8008decabae0)