Only use std::fma for fma

FMA should only be used for increase precision, and not
as a speed improvement. Having two versions of this
makes thinking about floating point error very difficult.

Change-Id: I59786b58837657c1e005ffc7bdc0bef5fe23cfd5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/721917
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
1 file changed