[graphite] fix graphite build with ganesh disabled

Change-Id: I11f509ee488b18e352c86ad5c3b1a7b921a142d8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1097602
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Thomas Smith <thomsmit@google.com>
2 files changed