fix up 16-bit formats for fp16

This is a mix of relaxing the test precision
and fixing the implementation (going via FP32).
I'm open to ideas for both sides of things.

Change-Id: I3b559bdb6857f6072e22ea06b536ef02640bb49e
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/215949
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
2 files changed