make skcms_TransferFunction_invert public

and clean up skcms_OptimizeForSpeed

Change-Id: I72a18b5981e63b6b029608b9394ea501b4c58ca7
Reviewed-on: https://skia-review.googlesource.com/157523
Auto-Submit: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
2 files changed