EGLContextCompatTest: fix typo in WindowDifferentConfig
EGLContextCompatTest: fix typo in WindowDifferentConfig

It was incorrectly calling the pbuffer function.

BUG=angleproject:891

Change-Id: I6959540262a8ef80886e41da795f9e4aff218535
Reviewed-on: https://chromium-review.googlesource.com/299441
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Tested-by: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@chromium.org>

domokit/waterfall,mlfarrell/angle,vvuk/angle,mikolalysenko/angle,MSOpenTech/angle,MSOpenTech/angle,mlfarrell/angle,vvuk/angle,mybios/angle,vvuk/angle,ecoal95/angle,domokit/waterfall,MSOpenTech/angle,mybios/angle,MSOpenTech/angle,mikolalysenko/angle,mikolalysenko/angle,ecoal95/angle,mybios/angle,mlfarrell/angle,ppy/angle,mikolalysenko/angle,ppy/angle,ecoal95/angle,vvuk/angle,ecoal95/angle,ppy/angle,ecoal95/angle,ppy/angle,mlfarrell/angle,mybios/angle