[graphite] Minor key generation fixes

Bug: b/259547998
Change-Id: I3cd56d0b16d0686d4026d0ae129b62367e288b9f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/615081
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
4 files changed