fixed uninitialized value in Perlin noise shader

Bug: skia:
Change-Id: Ie1670dd574b19faa396c8db1a58cfe922925ae5a
Reviewed-on: https://skia-review.googlesource.com/c/183386
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed