Simplify Perlin noise chained-if block.

We can use a single `step` rather than four separate if statements.

Change-Id: I472f63d497e8e5d7d5b7f37766a8fce871f8cef4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/694620
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
4 files changed