Fix GLSL int to float error in arc code in GrOvalRenderer.

BUG=skia:
TBR=robertphillips@google.com
NOTRY=true
NOTREECHECKS=true

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2263213004

Review-Url: https://codereview.chromium.org/2263213004
1 file changed