use fmaxf to prevent casting from and to double
use fmaxf to prevent casting from and to double

Summary:
Use ```fmaxf``` to prevent double casting.
Closes https://github.com/facebook/css-layout/pull/251

Reviewed By: emilsjolander

Differential Revision: D4199342

Pulled By: splhack

fbshipit-source-id: c04bc68a3c9c97b92e910e885457cf2fe00da28b

facebook/yoga,facebook/css-layout,yihuang/css-layout,yihuang/css-layout,rmarinho/yoga,facebook/yoga,facebook/css-layout,facebook/css-layout,facebook/yoga,yihuang/css-layout,facebook/yoga,facebook/css-layout,rmarinho/yoga,yihuang/css-layout,rmarinho/yoga,facebook/css-layout,facebook/yoga,yihuang/css-layout,yihuang/css-layout,yihuang/css-layout,yihuang/css-layout,rmarinho/yoga,facebook/css-layout,rmarinho/yoga,facebook/css-layout,facebook/css-layout,rmarinho/yoga,facebook/yoga,yihuang/css-layout,facebook/css-layout,yihuang/css-layout,rmarinho/yoga,facebook/yoga,facebook/yoga,rmarinho/yoga,rmarinho/yoga,facebook/yoga,rmarinho/yoga,facebook/yoga