scalarize SkGradientShader stop setup

One of Clankium's GCC 4.9 builds is crashing when compiling the
existing Sk4f version, so let's try ordinary scalar math.

BUG=chromium:721682

Change-Id: Ie37bf530ada537363119acd31814ae46cd3adf73
Reviewed-on: https://skia-review.googlesource.com/17210
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
1 file changed