Increase accuracy of float -> fixed in ICC code

Add a comment to SkFixed explaining the accuracy issues of the macros.

Bug: skia:
Change-Id: Ibfecb16821fefe87822cc3acd1cf8498df10a492
Reviewed-on: https://skia-review.googlesource.com/85742
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed