Hardcode offsets to zero in GrMockOpTarget

Change-Id: Ia091be9d84e6b338861997d3343f1112ca521c2b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/338200
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
1 file changed