Fix up arguments passed to pipeline.

  - Add half to (x,y) to get pixel centers.
  - The x updates were just totally wrong...

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4794
CQ_INCLUDE_TRYBOTS=master.client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Change-Id: I314489a74b54e2b88f12dd35896452ac0b9718f3
Reviewed-on: https://skia-review.googlesource.com/4794
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
1 file changed