switched SPIR-V vertexid to vertexindex

Bug: skia:
Change-Id: I32c10e2874feea63d7fa048057ef57e27d5874bc
Reviewed-on: https://skia-review.googlesource.com/115880
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
2 files changed