[graphite] Pass builder into SkShaderCodeDictionary::findOrCreate rather than the key

Just a minor cleanup to hide some cruft.

Bug: skia:12701
Change-Id: I70e9c8ba89a5b7d100a3d3f9b9dd084ad0a70715
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/548418
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
4 files changed