[skottie] Minor MotionBlurEffect cleanup

Change-Id: I9d02ff9f6bcc86cdc10e01a4e3379014557172e9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/244507
Commit-Queue: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Klein <mtklein@google.com>
2 files changed